553 5.1.3 Invalid address syntax

What the message looks like

• 553 5.1.3 Bad recipient address syntax
• 553 5.1.3 The recipient address is not a valid RFC 5321 address
• 501 5.1.3 Invalid address

What it means

The address isn't a valid email address, so the server rejected it without even looking it up. The standard name for this status is "bad destination mailbox address syntax".

Common causes

• Spaces, commas or semicolons inside the address, often from pasting a list of addresses into one field.
• Two @ signs, a missing @, or a missing domain.
• A trailing dot, or two dots in a row, such as john..doe@example.com.
• Hidden characters copied from a document or web page, such as a non-breaking space or a smart quote.
• Characters the receiving server doesn't accept, such as accented letters before the @.

If you're the recipient

Check the address you gave the sender. Type it out again instead of pasting it, in case it picked up a hidden character.

If you're the sender

Look closely at the address for spaces, extra dots and stray punctuation, then type it again by hand. If you're sending to several people, put each address in its own recipient field or separate them the way your email app expects.

If you use addy.io

addy.io aliases only accept plain ASCII characters before the @. If a sender tries an alias with accented or other non-ASCII characters, addy.io rejects it with 553 5.6.7 Non-ASCII characters in the local-part of the recipient address are not permitted. Create aliases using letters, numbers, dots, hyphens and underscores.