5.1.3 Bad destination mailbox address syntax

The address is written in a way that is not valid.

5.1.3 Bad destination mailbox address syntax

Permanent: retrying will not help

The address is written in a way that is not valid.

Usual causes

A stray space, comma, bracket or quote in the address.
Two @ signs, or none.

What to do

Clean the address and try again.
Validate addresses in your form before saving them.

Usually the fault of: sender.

Common questions.

What does 5.1.3 mean?

The address is written in a way that is not valid.

Will retrying fix 5.1.3?

No. It is a permanent failure, so retrying the same message will not help, and repeated attempts can hurt your sending reputation. Fix the cause first.

How do I fix 5.1.3?

Clean the address and try again. Validate addresses in your form before saving them.

Other codes: 5.1.1 · 5.1.2 · 5.1.6 · 5.2.1 · 5.2.2 · 5.2.3 · 5.3.4 · 5.4.1 · Decode a whole bounce message

See why every email bounced.

SendSend shows each message’s result, and the reason the receiving server gave. Free for 3,000 emails a month.

Get started free Check your domain