Gmail error: Receiving mail too fast?

Have you ever seen this SMTP error message?
450 4.2.1 The user you are trying to contact is receiving mail at a rate that prevents additional messages from being delivered. Please resend your message at a later time. If the user is able to receive mail at that time, your message will be delivered. For more information, go to Limits for sending & getting mail.

I certainly have! And somebody just reached out to me after running into it themselves. I’ve blogged about it before, but I thought it would be useful to address it again, with a bit more detail and clear links through to resolution, depending on the sending scenario.

What were you doing when you received this SMTP error message?
  1. You have configured your email platform to use BCC or archiving to send copies of every single email being sent, and you’re using a Gmail or Google Workspace account as the destination for all of those copies.
  2. You’re a software developer building an email application and as part of troubleshooting, you’re sending a duplicate copy of every outbound transactional email message to your test Gmail account, to make sure everything looks okay.
  3. You’re a software developer building an email application and as part of troubleshooting, you’re sending 10 email messages a minute to your test Gmail account, to make sure email is delivering properly.
  4. You’re doing inbox testing and so for every campaign, you’re including this address (and a number of others) in your send, every single time. Maybe dozens of times a day, maybe not.
  5. You’re a customer of an inbox testing platform, just trying to do your one inbox test, and you got this message when sending to the seed list.
  6. You’re trying to email your friend Bob. You’ve only sent one message to this address, so you have no idea what’s going on.
What should you do about this SMTP error message?
  1. Don’t use Gmail as a destination for email archiving. Gmail can’t keep up and they don’t want to facilitate this.
  2. You’re mailbombing your own test Gmail account. Don’t do this. Put limits in place to not do this type of email send any more than once every few minutes max.
  3. You’re mailbombing your own test Gmail account and could even end up causing legit emails to get blocked, if this mailbombing ends up affecting your IP or domain reputation at email. Don’t do this – it’s not a suitable way to monitor deliverability. Slow it down to one message an hour, one message a day, something like that.
  4. You might be sending so many inbox tests that it’s overloading the Gmail seed accounts. You may need to back off by sending fewer inbox tests, or pause longer between sends to the seed list.
  5. Your inbox testing provider’s seed list is overloaded based on activity by other customers. You’ll need to complain to them about that and see what they can do. Some providers can create seed accounts just for certain customers, to keep the seed addresses from being a shared resource with shared limits.
  6. Somebody’s mailbombing Bob right now, to the point that Gmail has stopped accepting additional inbound email for Bob. Give up for now, come back tomorrow and try again.
Want to learn more?
  • Gmail limits how many messages an account can receive per minute, per hour, per day. Learn more about those limits here.
  • Gmail also limits how many messages you can send in a day. They're a little opaque about this limits, as they can vary based on your sending reputation and their best guess as to whether or not you're trying to send spam.
  • Gmail is heavily invested in tracking domain reputation (and delaying or blocking certain messages based on domain reputation relating to DKIM, SPF, URLs, etc.) Learn more about those rejections here.
  • Find a full list of Gmail SMTP Errors and Codes here.

Happy sending, and don't forget that we've got a whole Gmail section here on Spam Resource, chock full of deliverability tips and tricks.

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