src/features/relays/RelaysPage.tsx

@@ -288,6 +288,7 @@ interface General {
   description: string;
   address: string;
   linkPort: string;
+  mxPreference: string;
   enabled: boolean;
   sendThrough: boolean;
   inboundOnly: boolean;
@@ -299,6 +300,7 @@ function general(relay: Relay): General {
     description: relay.description,
     address: relay.address,
     linkPort: String(relay.linkPort),
+    mxPreference: String(relay.mxPreference ?? 10),
     enabled: relay.enabled,
     sendThrough: relay.sendThrough,
     inboundOnly: relay.inboundOnly,
@@ -354,6 +356,13 @@ function SettingsDialog({
       }
       patch.linkPort = Number(g.linkPort);
     }
+    if (g.mxPreference !== startGeneral.mxPreference) {
+      if (!/^\d+$/.test(g.mxPreference) || Number(g.mxPreference) > 65535) {
+        setInvalid('mxPreference');
+        return;
+      }
+      patch.mxPreference = Number(g.mxPreference);
+    }
     for (const flag of ['enabled', 'sendThrough', 'inboundOnly'] as const) {
       if (g[flag] !== startGeneral[flag]) patch[flag] = g[flag];
     }
@@ -443,9 +452,20 @@ function SettingsDialog({
 
         <section className="space-y-3">
           <h3 className="text-sm font-medium">{t('relays.s.receiving', 'Taking mail in')}</h3>
-          <Field field="hostname" label={t('relays.f.hostname', 'Public name')}>
-            {input('hostname', { placeholder: 'mx1.example.com' })}
-          </Field>
+          <div className="grid grid-cols-[1fr_8rem] gap-3">
+            <Field field="hostname" label={t('relays.f.hostname', 'Public name')}>
+              {input('hostname', { placeholder: 'mx1.example.com' })}
+            </Field>
+            <Field field="mxPreference" label={t('relays.f.mxPreference', 'MX preference')}>
+              <Input
+                value={g.mxPreference}
+                inputMode="numeric"
+                disabled={!canChange}
+                aria-invalid={invalid === 'mxPreference'}
+                onChange={(e) => setG({ ...g, mxPreference: e.target.value })}
+              />
+            </Field>
+          </div>
           <Field field="smtpListen" label={t('relays.f.smtpListen', 'Listens on')}>
             {input('smtpListen', { placeholder: '[::]:25' })}
           </Field>

src/features/relays/model.test.ts

@@ -69,6 +69,7 @@ function relay(extra: Partial<Relay> = {}): Relay {
     enabled: true,
     sendThrough: false,
     inboundOnly: false,
+    mxPreference: 10,
     settings: SETTINGS,
     joinState: 'joined',
     links: [link('1')],

src/features/relays/model.ts

@@ -63,6 +63,8 @@ export interface Relay {
   enabled: boolean;
   sendThrough: boolean;
   inboundOnly: boolean;
+  /** Absent from servers before RL-25. */
+  mxPreference?: number;
   settings: RelaySettings;
   joinState: 'waiting' | 'expired' | 'joined';
   joinExpiresAt?: string | null;

src/help/texts.ts

@@ -25,13 +25,15 @@ export const FIELD_HELP: Record<string, string> = {
     'The relay’s host name or IP address, as this server dials it for the link. A WireGuard address keeps the link off the internet.',
   'inbuxa:Relay.linkPort': 'The port the relay listens on for this server’s link. 443 unless you chose another.',
   'inbuxa:Relay.enabled':
-    'Turn off to drop the link: the relay closes port 25 and keeps what it holds until it’s turned back on.',
+    'Turn off to stop this server linking to it. The relay keeps the mail it holds and goes on taking mail in, held until it’s turned back on.',
   'inbuxa:Relay.sendThrough':
     'Send all outgoing mail through relays instead of straight from this server. Mail waits here while no relay is linked.',
   'inbuxa:Relay.inboundOnly':
     'The relay takes mail in but sends none, for instance while its address is new to other providers or not in your SPF record yet.',
   'inbuxa:Relay.hostname':
-    'The relay’s public name: what it says when other servers connect, and the name on its certificate. Needs an A record and matching reverse DNS.',
+    'The relay’s public name: what it says when other servers connect, and the name on its certificate. Needs an A record and matching reverse DNS. Where this server publishes a domain’s DNS, it’s in the MX and SPF records.',
+  'inbuxa:Relay.mxPreference':
+    'Where this server publishes a domain’s DNS, the relay’s MX preference: senders try the lowest first. Give relays the same number to share the mail.',
   'inbuxa:Relay.smtpListen': 'The addresses the relay takes mail on, usually [::]:25 for every address on port 25.',
   'inbuxa:Relay.maxMessageSize': 'The largest message the relay accepts, in either direction.',
   'inbuxa:Relay.maxRecipients': 'How many recipients one message may have at the relay.',

src/i18n/en.json

@@ -2388,7 +2388,8 @@
       "spoolMaxBytes": "Spool size (GB)",
       "outboundRetry": "Waits between attempts",
       "outboundExpiry": "Give up after",
-      "outboundTls": "Encryption"
+      "outboundTls": "Encryption",
+      "mxPreference": "MX preference"
     },
     "cancel": "Cancel",
     "addGo": "Add",