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Gmail with >10 recipients is refused Mailtrap SMTP connections

Email API/SMTP

A single email sent from Gmail with more than 10 recipients spawns more than 10 SMTP connections to Mailtrap, resulting in errors.

535 5.7.8 Too many connections per account

Mailtrap limits the number of concurrent SMTP connections per account to 10. https://help.mailtrap.io/article/100-sending-limits

Gmail breaks an email to 20 recipients into 20 emails to a single recipient and creates an SMTP connection for each of those emails.

I am using Gmail in a web browser with "Send mail as" configured to send an email from my domain via live.smtp.mailtrap.io. I first noticed the issue using https://www.mailreach.co/email-spam-test (30 recipients), but it's easy to replicate by sending any test email with 11 or more recipients.

This is really a Gmail problem: their use of SMTP connections is horrible. However, Mailtrap might want to consider something to accommodate it.

Also, there's no indication on Maitrap's Stats page that SMTP connections were refused, it gives the impression that everything is fine.

Posted by kingfisher ·
Status: Rejected1 comment

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Comments1

  • Mailtrap Product Team

    Team•

    Oct 27, 2025

    hi @kingfisher , thanks for the input!

    We understand the issue, but our primary goal is to be used from the code, not in Gmail integration. In that case the most SMTP clients allow to configure max number of SMTP connection and max number of emails per each.

    As for not having an error in the logs: it’s intended to be so. As in Logs you see messages those have been processed/billed, and refusing due to the number of connection is one step ahead of email processing.

    We also are able to manually adjust max number of connections, but only for Business and higher plans.