implement a catchall address for a domain

by specifying a "destination" in an account that is just "@" followed by the
domain, e.g. "@example.org". messages are only delivered to the catchall
address when no regular destination matches (taking the per-domain
catchall-separator and case-sensisitivity into account).

for issue #18

.gitignore

@@ -16,6 +16,7 @@
 /testdata/smtp/data/
 /testdata/smtp/datajunk/
 /testdata/smtp/sendlimit/data/
+/testdata/smtp/catchall/data/
 /testdata/store/data/
 /testdata/train/
 /cover.out

config/config.go

@@ -232,7 +232,7 @@ type DKIM struct {
 type Account struct {
 	Domain       string                 `sconf-doc:"Default domain for account. Deprecated behaviour: If a destination is not a full address but only a localpart, this domain is added to form a full address."`
 	Description  string                 `sconf:"optional" sconf-doc:"Free form description, e.g. full name or alternative contact info."`
-	Destinations map[string]Destination `sconf-doc:"Destinations, keys are email addresses (with IDNA domains). Deprecated behaviour: If the address is not a full address but a localpart, it is combined with Domain to form a full address."`
+	Destinations map[string]Destination `sconf-doc:"Destinations, keys are email addresses (with IDNA domains). If the address is of the form '@domain', i.e. with localpart missing, it serves as a catchall for the domain, matching all messages that are not explicitly configured. Deprecated behaviour: If the address is not a full address but a localpart, it is combined with Domain to form a full address."`
 	SubjectPass  struct {
 		Period time.Duration `sconf-doc:"How long unique values are accepted after generating, e.g. 12h."` // todo: have a reasonable default for this?
 	} `sconf:"optional" sconf-doc:"If configured, messages classified as weakly spam are rejected with instructions to retry delivery, but this time with a signed token added to the subject. During the next delivery attempt, the signed token will bypass the spam filter. Messages with a clear spam signal, such as a known bad reputation, are rejected/delayed without a signed token."`

config/doc.go

@@ -468,7 +468,9 @@ describe-static" and "mox config describe-domains":
 			# Free form description, e.g. full name or alternative contact info. (optional)
 			Description:
 
-			# Destinations, keys are email addresses (with IDNA domains). Deprecated
+			# Destinations, keys are email addresses (with IDNA domains). If the address is of
+			# the form '@domain', i.e. with localpart missing, it serves as a catchall for the
+			# domain, matching all messages that are not explicitly configured. Deprecated
 			# behaviour: If the address is not a full address but a localpart, it is combined
 			# with Domain to form a full address.
 			Destinations:

doc.go

@@ -404,13 +404,16 @@ these addresses will be rejected.
 
 Adds an address to an account and reloads the configuration.
 
+If address starts with a @ (i.e. a missing localpart), this is a catchall
+address for the domain.
+
 	usage: mox config address add address account
 
 # mox config address rm
 
 Remove an address and reload the configuration.
 
-Incoming email for this address will be rejected.
+Incoming email for this address will be rejected after removing an address.
 
 	usage: mox config address rm address
 

http/account.html

@@ -273,6 +273,7 @@ const index = async () => {
 			Object.entries(destinations).sort().map(t =>
 				dom.li(
 					dom.a(t[0], attr({href: '#destinations/'+t[0]})),
+					t[0].startsWith('@') ? ' (catchall)' : [],
 				),
 			),
 		),

http/admin.go

@@ -1126,8 +1126,8 @@ func (Admin) Domain(ctx context.Context, domain string) dns.Domain {
 	return d
 }
 
-// DomainLocalparts returns the localparts and accounts configured in domain.
+// DomainLocalparts returns the encoded localparts and accounts configured in domain.
-func (Admin) DomainLocalparts(ctx context.Context, domain string) (localpartAccounts map[smtp.Localpart]string) {
+func (Admin) DomainLocalparts(ctx context.Context, domain string) (localpartAccounts map[string]string) {
 	d, err := dns.ParseDomain(domain)
 	xcheckf(ctx, err, "parsing domain")
 	_, ok := mox.Conf.Domain(d)

http/admin.html

@@ -509,6 +509,9 @@ const account = async (name) => {
 							lp, '@',
 							dom.a(d, attr({href: '#domains/'+d})),
 						]
+						if (lp === '') {
+							v.unshift('(catchall) ')
+						}
 					}
 					return dom.tr(
 						dom.td(v),
@@ -568,9 +571,9 @@ const account = async (name) => {
 			fieldset=dom.fieldset(
 				dom.label(
 					style({display: 'inline-block'}),
-					'Email address or localpart',
+					dom.span('Email address or localpart', attr({title: 'If empty, or localpart is empty, a catchall address is configured for the domain.'})),
 					dom.br(),
-					email=dom.input(attr({required: ''})),
+					email=dom.input(),
 				),
 				' ',
 				dom.button('Add address'),
@@ -748,7 +751,7 @@ const domain = async (d) => {
 			dom.tbody(
 				Object.entries(localpartAccounts).map(t =>
 					dom.tr(
-						dom.td(t[0]),
+						dom.td(t[0] || '(catchall)'),
 						dom.td(dom.a(t[1], attr({href: '#accounts/'+t[1]}))),
 						dom.td(
 							dom.button('Remove address', async function click(e) {
@@ -758,7 +761,7 @@ const domain = async (d) => {
 								}
 								e.target.disabled = true
 								try {
-									await api.AddressRemove(t[0] + '@'+d)
+									await api.AddressRemove(t[0] + '@' + d)
 								} catch (err) {
 									console.log({err})
 									window.alert('Error: ' + err.message)
@@ -795,9 +798,9 @@ const domain = async (d) => {
 			fieldset=dom.fieldset(
 				dom.label(
 					style({display: 'inline-block'}),
-					'Localpart',
+					dom.span('Localpart', attr({title: 'An empty localpart is the catchall destination/address for the domain.'})),
 					dom.br(),
-					localpart=dom.input(attr({required: ''})),
+					localpart=dom.input(),
 				),
 				' ',
 				dom.label(

http/adminapi.json

@@ -58,7 +58,7 @@
 		},
 		{
 			"Name": "DomainLocalparts",
-			"Docs": "DomainLocalparts returns the localparts and accounts configured in domain.",
+			"Docs": "DomainLocalparts returns the encoded localparts and accounts configured in domain.",
 			"Params": [
 				{
 					"Name": "domain",
@@ -3237,11 +3237,6 @@
 				}
 			]
 		},
-		{
-			"Name": "Localpart",
-			"Docs": "Localpart is a decoded local part of an email address, before the \"@\".\nFor quoted strings, values do not hold the double quote or escaping backslashes.\nAn empty string can be a valid localpart.",
-			"Values": null
-		},
 		{
 			"Name": "ResultType",
 			"Docs": "ResultType represents a TLS error.",
@@ -3490,6 +3485,11 @@
 				}
 			]
 		},
+		{
+			"Name": "Localpart",
+			"Docs": "Localpart is a decoded local part of an email address, before the \"@\".\nFor quoted strings, values do not hold the double quote or escaping backslashes.\nAn empty string can be a valid localpart.",
+			"Values": null
+		},
 		{
 			"Name": "IP",
 			"Docs": "An IP is a single IP address, a slice of bytes.\nFunctions in this package accept either 4-byte (IPv4)\nor 16-byte (IPv6) slices as input.\n\nNote that in this documentation, referring to an\nIP address as an IPv4 address or an IPv6 address\nis a semantic property of the address, not just the\nlength of the byte slice: a 16-byte slice can still\nbe an IPv4 address.",

main.go

@@ -655,7 +655,11 @@ these addresses will be rejected.
 
 func cmdConfigAddressAdd(c *cmd) {
 	c.params = "address account"
-	c.help = "Adds an address to an account and reloads the configuration."
+	c.help = `Adds an address to an account and reloads the configuration.
+
+If address starts with a @ (i.e. a missing localpart), this is a catchall
+address for the domain.
+`
 	args := c.Parse()
 	if len(args) != 2 {
 		c.Usage()
@@ -675,7 +679,7 @@ func cmdConfigAddressRemove(c *cmd) {
 	c.params = "address"
 	c.help = `Remove an address and reload the configuration.
 
-Incoming email for this address will be rejected.
+Incoming email for this address will be rejected after removing an address.
 `
 	args := c.Parse()
 	if len(args) != 1 {

mox-/admin.go

@@ -555,6 +555,8 @@ func DomainRecords(domConf config.Domain, domain dns.Domain) ([]string, error) {
 //
 // The new account does not have a password, so cannot yet log in. Email can be
 // delivered.
+//
+// Catchall addresses are not supported for AccountAdd. Add separately with AddressAdd.
 func AccountAdd(ctx context.Context, account, address string) (rerr error) {
 	log := xlog.WithContext(ctx)
 	defer func() {
@@ -648,8 +650,8 @@ func checkAddressAvailable(addr smtp.Address) error {
 	return nil
 }
 
-// AddressAdd adds an email address to an account and reloads the
+// AddressAdd adds an email address to an account and reloads the configuration. If
-// configuration.
+// address starts with an @ it is treated as a catchall address for the domain.
 func AddressAdd(ctx context.Context, address, account string) (rerr error) {
 	log := xlog.WithContext(ctx)
 	defer func() {
@@ -658,11 +660,6 @@ func AddressAdd(ctx context.Context, address, account string) (rerr error) {
 		}
 	}()
 
-	addr, err := smtp.ParseAddress(address)
-	if err != nil {
-		return fmt.Errorf("parsing email address: %v", err)
-	}
-
 	Conf.dynamicMutex.Lock()
 	defer Conf.dynamicMutex.Unlock()
 
@@ -672,9 +669,30 @@ func AddressAdd(ctx context.Context, address, account string) (rerr error) {
 		return fmt.Errorf("account does not exist")
 	}
 
+	var destAddr string
+	if strings.HasPrefix(address, "@") {
+		d, err := dns.ParseDomain(address[1:])
+		if err != nil {
+			return fmt.Errorf("parsing domain: %v", err)
+		}
+		dname := d.Name()
+		destAddr = "@" + dname
+		if _, ok := Conf.Dynamic.Domains[dname]; !ok {
+			return fmt.Errorf("domain does not exist")
+		} else if _, ok := Conf.accountDestinations[destAddr]; ok {
+			return fmt.Errorf("catchall address already configured for domain")
+		}
+	} else {
+		addr, err := smtp.ParseAddress(address)
+		if err != nil {
+			return fmt.Errorf("parsing email address: %v", err)
+		}
+
 		if err := checkAddressAvailable(addr); err != nil {
 			return fmt.Errorf("address not available: %v", err)
 		}
+		destAddr = addr.String()
+	}
 
 	// Compose new config without modifying existing data structures. If we fail, we
 	// leave no trace.
@@ -687,14 +705,14 @@ func AddressAdd(ctx context.Context, address, account string) (rerr error) {
 	for name, d := range a.Destinations {
 		nd[name] = d
 	}
-	nd[addr.String()] = config.Destination{}
+	nd[destAddr] = config.Destination{}
 	a.Destinations = nd
 	nc.Accounts[account] = a
 
 	if err := writeDynamic(ctx, log, nc); err != nil {
 		return fmt.Errorf("writing domains.conf: %v", err)
 	}
-	log.Info("address added", mlog.Field("address", addr), mlog.Field("account", account))
+	log.Info("address added", mlog.Field("address", address), mlog.Field("account", account))
 	return nil
 }
 
@@ -710,31 +728,23 @@ func AddressRemove(ctx context.Context, address string) (rerr error) {
 	Conf.dynamicMutex.Lock()
 	defer Conf.dynamicMutex.Unlock()
 
-	c := Conf.Dynamic
+	ad, ok := Conf.accountDestinations[address]
-
-	addr, err := smtp.ParseAddress(address)
-	if err != nil {
-		return fmt.Errorf("parsing email address: %v", err)
-	}
-	ad, ok := Conf.accountDestinations[addr.String()]
 	if !ok {
 		return fmt.Errorf("address does not exists")
 	}
-	addrStr := addr.String()
 
 	// Compose new config without modifying existing data structures. If we fail, we
 	// leave no trace.
-	a, ok := c.Accounts[ad.Account]
+	a, ok := Conf.Dynamic.Accounts[ad.Account]
 	if !ok {
 		return fmt.Errorf("internal error: cannot find account")
 	}
 	na := a
 	na.Destinations = map[string]config.Destination{}
 	var dropped bool
-	for name, d := range a.Destinations {
+	for destAddr, d := range a.Destinations {
-		// todo deprecated: remove support for localpart-only with default domain as destination address.
+		if destAddr != address {
-		if !(name == addr.Localpart.String() && a.DNSDomain == addr.Domain || name == addrStr) {
+			na.Destinations[destAddr] = d
-			na.Destinations[name] = d
 		} else {
 			dropped = true
 		}
@@ -742,9 +752,9 @@ func AddressRemove(ctx context.Context, address string) (rerr error) {
 	if !dropped {
 		return fmt.Errorf("address not removed, likely a postmaster/reporting address")
 	}
-	nc := c
+	nc := Conf.Dynamic
 	nc.Accounts = map[string]config.Account{}
-	for name, a := range c.Accounts {
+	for name, a := range Conf.Dynamic.Accounts {
 		nc.Accounts[name] = a
 	}
 	nc.Accounts[ad.Account] = na
@@ -752,7 +762,7 @@ func AddressRemove(ctx context.Context, address string) (rerr error) {
 	if err := writeDynamic(ctx, log, nc); err != nil {
 		return fmt.Errorf("writing domains.conf: %v", err)
 	}
-	log.Info("address removed", mlog.Field("address", addr), mlog.Field("account", ad.Account))
+	log.Info("address removed", mlog.Field("address", address), mlog.Field("account", ad.Account))
 	return nil
 }
 

mox-/config.go

@@ -67,7 +67,8 @@ type Config struct {
 }
 
 type AccountDestination struct {
-	Localpart   smtp.Localpart
+	Catchall    bool           // If catchall destination for its domain.
+	Localpart   smtp.Localpart // In original casing as written in config file.
 	Account     string
 	Destination config.Destination
 }
@@ -167,13 +168,19 @@ func (c *Config) Accounts() (l []string) {
 	return
 }
 
-func (c *Config) DomainLocalparts(d dns.Domain) map[smtp.Localpart]string {
+// DomainLocalparts returns a mapping of encoded localparts to account names for a
+// domain. An empty localpart is a catchall destination for a domain.
+func (c *Config) DomainLocalparts(d dns.Domain) map[string]string {
 	suffix := "@" + d.Name()
-	m := map[smtp.Localpart]string{}
+	m := map[string]string{}
 	c.withDynamicLock(func() {
 		for addr, ad := range c.accountDestinations {
 			if strings.HasSuffix(addr, suffix) {
-				m[ad.Localpart] = ad.Account
+				if ad.Catchall {
+					m[""] = ad.Account
+				} else {
+					m[ad.Localpart.String()] = ad.Account
+				}
 			}
 		}
 	})
@@ -685,7 +692,7 @@ func prepareDynamicConfig(ctx context.Context, dynamicPath string, static config
 		errs = append(errs, fmt.Errorf(format, args...))
 	}
 
-	// check that mailbox is in unicode NFC normalized form.
+	// Check that mailbox is in unicode NFC normalized form.
 	checkMailboxNormf := func(mailbox string, format string, args ...any) {
 		s := norm.NFC.String(mailbox)
 		if mailbox != s {
@@ -930,10 +937,27 @@ func prepareDynamicConfig(ctx context.Context, dynamicPath string, static config
 				}
 			}
 
+			// Catchall destination for domain.
+			if strings.HasPrefix(addrName, "@") {
+				d, err := dns.ParseDomain(addrName[1:])
+				if err != nil {
+					addErrorf("parsing domain %q in account %q", addrName[1:], accName)
+					continue
+				} else if _, ok := c.Domains[d.Name()]; !ok {
+					addErrorf("unknown domain for address %q in account %q", addrName, accName)
+					continue
+				}
+				addrFull := "@" + d.Name()
+				if _, ok := accDests[addrFull]; ok {
+					addErrorf("duplicate canonicalized catchall destination address %s", addrFull)
+				}
+				accDests[addrFull] = AccountDestination{true, "", accName, dest}
+				continue
+			}
+
 			// todo deprecated: remove support for parsing destination as just a localpart instead full address.
 			var address smtp.Address
-			localpart, err := smtp.ParseLocalpart(addrName)
+			if localpart, err := smtp.ParseLocalpart(addrName); err != nil && errors.Is(err, smtp.ErrBadLocalpart) {
-			if err != nil && errors.Is(err, smtp.ErrBadLocalpart) {
 				address, err = smtp.ParseAddress(addrName)
 				if err != nil {
 					addErrorf("invalid email address %q in account %q", addrName, accName)
@@ -955,6 +979,7 @@ func prepareDynamicConfig(ctx context.Context, dynamicPath string, static config
 				replaceLocalparts[addrName] = address.Pack(true)
 			}
 
+			origLP := address.Localpart
 			dc := c.Domains[address.Domain.Name()]
 			if lp, err := CanonicalLocalpart(address.Localpart, dc); err != nil {
 				addErrorf("canonicalizing localpart %s: %v", address.Localpart, err)
@@ -967,7 +992,7 @@ func prepareDynamicConfig(ctx context.Context, dynamicPath string, static config
 			if _, ok := accDests[addrFull]; ok {
 				addErrorf("duplicate canonicalized destination address %s", addrFull)
 			}
-			accDests[addrFull] = AccountDestination{address.Localpart, accName, dest}
+			accDests[addrFull] = AccountDestination{false, origLP, accName, dest}
 		}
 
 		for lp, addr := range replaceLocalparts {
@@ -1007,7 +1032,7 @@ func prepareDynamicConfig(ctx context.Context, dynamicPath string, static config
 			DMARCReports: true,
 		}
 		checkMailboxNormf(dmarc.Mailbox, "DMARC mailbox for account %q", dmarc.Account)
-		accDests[addrFull] = AccountDestination{lp, dmarc.Account, dest}
+		accDests[addrFull] = AccountDestination{false, lp, dmarc.Account, dest}
 	}
 
 	// Set TLSRPT destinations.
@@ -1036,7 +1061,7 @@ func prepareDynamicConfig(ctx context.Context, dynamicPath string, static config
 			TLSReports: true,
 		}
 		checkMailboxNormf(tlsrpt.Mailbox, "TLSRPT mailbox for account %q", tlsrpt.Account)
-		accDests[addrFull] = AccountDestination{lp, tlsrpt.Account, dest}
+		accDests[addrFull] = AccountDestination{false, lp, tlsrpt.Account, dest}
 	}
 
 	// Check webserver configs.

mox-/lookup.go

@@ -43,8 +43,11 @@ func FindAccount(localpart smtp.Localpart, domain dns.Domain, allowPostmaster bo
 
 	accAddr, ok := Conf.AccountDestination(canonical)
 	if !ok {
+		if accAddr, ok = Conf.AccountDestination("@" + domain.Name()); !ok {
 			return "", "", config.Destination{}, ErrAccountNotFound
 		}
+		canonical = "@" + domain.Name()
+	}
 	return accAddr.Account, canonical, accAddr.Destination, nil
 }
 

smtpserver/server.go

@@ -1625,7 +1625,7 @@ func messageHeaderCommentDomain(domain dns.Domain, smtputf8 bool) string {
 	return s
 }
 
-// submit is used for incoming mail from authenticated users.
+// submit is used for mail from authenticated users that we will try to deliver.
 func (c *conn) submit(ctx context.Context, recvHdrFor func(string) string, msgWriter *message.Writer, pdataFile **os.File) {
 	dataFile := *pdataFile
 

smtpserver/server_test.go

@@ -958,3 +958,48 @@ func TestLimitOutgoing(t *testing.T) {
 	testSubmit("b@other.example", nil)
 	testSubmit("b@other.example", &smtpclient.Error{Code: smtp.C451LocalErr, Secode: smtp.SePol7DeliveryUnauth1}) // Would be 5th message.
 }
+
+// Test with catchall destination address.
+func TestCatchall(t *testing.T) {
+	resolver := dns.MockResolver{
+		A: map[string][]string{
+			"other.example.": {"127.0.0.10"}, // For mx check.
+		},
+		PTR: map[string][]string{
+			"127.0.0.10": {"other.example."},
+		},
+	}
+	ts := newTestServer(t, "../testdata/smtp/catchall/mox.conf", resolver)
+	defer ts.close()
+
+	testDeliver := func(rcptTo string, expErr *smtpclient.Error) {
+		t.Helper()
+		ts.run(func(err error, client *smtpclient.Client) {
+			t.Helper()
+			mailFrom := "mjl@other.example"
+			if err == nil {
+				err = client.Deliver(context.Background(), mailFrom, rcptTo, int64(len(submitMessage)), strings.NewReader(submitMessage), false, false)
+			}
+			var cerr smtpclient.Error
+			if expErr == nil && err != nil || expErr != nil && (err == nil || !errors.As(err, &cerr) || cerr.Secode != expErr.Secode) {
+				t.Fatalf("got err %#v, expected %#v", err, expErr)
+			}
+		})
+	}
+
+	testDeliver("mjl@mox.example", nil)      // Exact match.
+	testDeliver("mjl+test@mox.example", nil) // Domain localpart catchall separator.
+	testDeliver("MJL+TEST@mox.example", nil) // Again, and case insensitive.
+	testDeliver("unknown@mox.example", nil)  // Catchall address, to account catchall.
+
+	n, err := bstore.QueryDB[store.Message](ts.acc.DB).Count()
+	tcheck(t, err, "checking delivered messages")
+	tcompare(t, n, 3)
+
+	acc, err := store.OpenAccount("catchall")
+	tcheck(t, err, "open account")
+	defer acc.Close()
+	n, err = bstore.QueryDB[store.Message](acc.DB).Count()
+	tcheck(t, err, "checking delivered messages to catchall account")
+	tcompare(t, n, 1)
+}

testdata/smtp/catchall/domains.conf

@@ -0,0 +1,12 @@
+Domains:
+	mox.example:
+		LocalpartCatchallSeparator: +
+Accounts:
+	mjl:
+		Domain: mox.example
+		Destinations:
+			mjl@mox.example: nil
+	catchall:
+		Domain: mox.example
+		Destinations:
+			@mox.example: nil

testdata/smtp/catchall/mox.conf

@@ -0,0 +1,9 @@
+DataDir: data
+User: 1000
+LogLevel: trace
+Hostname: mox.example
+Postmaster:
+	Account: mjl
+	Mailbox: postmaster
+Listeners:
+	local: nil