Tip: cutting bounces from comment subscriptions
Posted: Mon Nov 02, 2026 3:18 pm
Hi everyone,
Disclosure first: I work for SendBridge, an email verification service (linked below). The tips below work with any verifier, and steps 2 and 3 need no external service at all.
Readers who comment with "Subscribe to this entry" ticked sometimes type the address wrong ("gmial.com") or use a throwaway inbox. Serendipity then sends notification emails to addresses that don't exist. The bounces go to the blog's mail account, and with enough of them your host or mail provider may start rate-limiting or spam-flagging the blog's outgoing mail, including the notifications that matter.
What helps:
1. Find the bad addresses already stored
Comment subscriptions live in the comments table, so a quick query shows who is subscribed:
(Adjust the table prefix if yours isn't "serendipity_".) Run that list through an email verifier (ours is SendBridge's email verification service, but any similar service works). It checks MX records and whether the mailbox actually exists, and returns valid / invalid / disposable / catch-all for each address. Then unsubscribe the invalid ones:
2. Stop new ones at the door
The Spam Protector (spamblock) plugin can require an email address and has a filter list for email addresses. Adding the most common throwaway domains (mailinator, guerrillamail, 10minutemail, yopmail and so on) there removes most of the junk subscriptions.
3. Watch the bounce mailbox
Make sure the blog's sender address is a real mailbox and look at it once a month. If the same reader bounces twice, unsubscribe them.
If someone wants to build this into a proper event plugin (an API check when a comment is saved), I'd be happy to help test it.
Peter Braun (SendBridge)
Disclosure first: I work for SendBridge, an email verification service (linked below). The tips below work with any verifier, and steps 2 and 3 need no external service at all.
Readers who comment with "Subscribe to this entry" ticked sometimes type the address wrong ("gmial.com") or use a throwaway inbox. Serendipity then sends notification emails to addresses that don't exist. The bounces go to the blog's mail account, and with enough of them your host or mail provider may start rate-limiting or spam-flagging the blog's outgoing mail, including the notifications that matter.
What helps:
1. Find the bad addresses already stored
Comment subscriptions live in the comments table, so a quick query shows who is subscribed:
Code: Select all
SELECT DISTINCT email FROM serendipity_comments WHERE subscribed = 'true' AND email <> '';Code: Select all
UPDATE serendipity_comments SET subscribed = 'false' WHERE email IN ('dead@example.com', '...');The Spam Protector (spamblock) plugin can require an email address and has a filter list for email addresses. Adding the most common throwaway domains (mailinator, guerrillamail, 10minutemail, yopmail and so on) there removes most of the junk subscriptions.
3. Watch the bounce mailbox
Make sure the blog's sender address is a real mailbox and look at it once a month. If the same reader bounces twice, unsubscribe them.
If someone wants to build this into a proper event plugin (an API check when a comment is saved), I'd be happy to help test it.
Peter Braun (SendBridge)