SMTP 550

In short: The mail server rejects the e-mail permanently (for example recipient does not exist).

In more detail: 550 belongs to the permanent errors (5xx).

In Depth

Possible causes

• Recipient address wrong.
• Sender classified as spam or SPF/DKIM missing.
• Mailbox full or blocked.

Solutions

1. Check the address.
2. Set up the sender domain with SPF, DKIM and DMARC.
3. Check the entry if on a blocklist.

See also: SMTP, Spam E-mail, DNS