Did anyone get the message?

Usually yes. Recipients accepted before the limit was reached get the message; only the rejected addresses appear in the bounce.

What limit should I aim for?

Limits vary by provider and plan, often between 50 and 1000 per message. Batching at 50 or fewer, or one recipient per message, avoids the problem everywhere.

5.5.3 bounce: too many recipients

5.5.3Too many recipientsPermanent: retrying will not help

Example

452 4.5.3 Error: too many recipients

What it means

X.5.3 in RFC 3463 is “too many recipients”: the server will not accept more RCPT TO commands for this transaction. Postfix sends 452 4.5.3 once its recipient limit for a single message is reached, and RFC 5321 expects compliant clients to send the rest in a new transaction.

The class digit matters here. With 4.5.3 on a RCPT command, a correct MTA delivers the accepted recipients now and retries the remainder in a later transaction, so nobody loses mail. A 5.5.3 means the server, or a relay in front of it, refused the extra recipients permanently and they bounce.

Do not confuse this with a sending quota. A daily cap on recipients per account usually comes back as a 4.7.x or 5.7.x policy reply or a provider-specific text, not as X.5.3, which only ever concerns one SMTP transaction.

Likely causes

A message addressed to hundreds of people in To, Cc and Bcc, sent through a server with a lower per-message recipient limit.
A web application or CRM that puts a whole mailing list into a single message instead of one message per recipient.
A client that treats the 452 reply as fatal instead of opening a new transaction for the remaining recipients.
A low limit configured on your own outbound relay (for example Postfix `smtpd_recipient_limit`) that rejects the message before it leaves.

How to fix it

Read the bounce to see which recipients were refused; the ones listed before the limit were usually delivered.
Split large sends into batches below the receiver’s limit, or better, send one message per recipient through a proper bulk tool.
If your own relay produced the code, raise its limit (Postfix: `smtpd_recipient_limit = 1000`) only as far as your downstream providers allow.
Make sure your sending software handles 452 on RCPT by deferring the extra recipients rather than bouncing them.

Checks that apply

Your domain or sending IP (fills in the checks below)

SMTP Diagnostics Confirms which server answers for the domain, so you know whose recipient limit you are hitting.
Google/Yahoo Compliance If you are mass mailing Gmail or Yahoo users, shows whether you meet bulk-sender rules before you split the list into many messages.

FAQ

Did anyone get the message?: Usually yes. Recipients accepted before the limit was reached get the message; only the rejected addresses appear in the bounce.
What limit should I aim for?: Limits vary by provider and plan, often between 50 and 1000 per message. Batching at 50 or fewer, or one recipient per message, avoids the problem everywhere.

All 191 bounce codes