SendGrid 550 mailbox unavailable / 551 / 553: hard bounces, remove the address
Shows how to fix sendGrid 550 mailbox unavailable / 551 / 553: hard bounces, remove the address. Use it when you hit this exact problem. Skip it when your error message or symptom looks different.
TL;DR
Remove the address from the mailing list.
Steps
- Symptom: bounce events or SMTP replies with 550 mailbox unavailable, 551, or 553.
- Treat these as hard bounces. The address does not exist or will never accept mail. Retrying is pointless and hurts reputation.
- Remove the address from the mailing list. SendGrid's own guidance for all three codes is the same: take them off the list.
- If you keep mailing a bounced address, SendGrid suppresses it for you (the bounce suppression list) and logs a repeat-bounce drop. Clean your list before SendGrid has to.
- Distinguish from 421/450/451 deferrals, which are temporary and retried for up to 72 hours. 5xx is permanent, 4xx is temporary.
- A sudden burst of 550s on previously good addresses means a typo in the recipient source, a bad import, or a compromised signup form, not a SendGrid outage. Check the source.
- Wire the Event Webhook bounce events into your list management so hard bounces unsubscribe automatically.
When to use
You are seeing this: Symptom: bounce events or SMTP replies with 550 mailbox unavailable, 551, or 553. Use this skill when you run into "SendGrid 550 mailbox unavailable / 551 / 553: hard bounces, remove the address".
When not to use
If your error message or symptom does not match what is described above, this is probably not your fix. Search for your exact error text instead of forcing this one to fit.
Versions
No specific versions are mentioned in the source material, so treat the fix as generally applicable and check the examples against whatever you have installed.
Why this happens
The original report does not dig into a root cause. It documents the symptom and the fix that resolved it.