- What does '550' mean in a mail delivery failure?
- 550 is a permanent SMTP rejection code meaning the recipient's mail server refused the message and will not retry. Common reasons: the recipient address doesn't exist, the server has spam filters blocking you, or you've been added to a blocklist.
- How do I find out exactly why I was rejected?
- Read the full bounce message — it usually includes more detail after '550', such as '550 5.1.1 The email account that you tried to reach does not exist' (wrong address) or '550 5.7.1 Message rejected' (spam filter). That sub-code identifies the exact cause.
- Can I get off an email blocklist?
- If you're sending from a personal address, contact your ISP or email provider — they manage the reputation of your sending IP. If it's a business email, check mxtoolbox.com to see which blocklists you're on and follow their delisting instructions.