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Fixing the 550 5.7.1 [STF] Sending too fast error

If you have received this error message, your account, script, or program has suddenly increased its sending rate. This may indicate your account has been compromised.

One of the tell-tale signs of a spam attack is a sudden change in email volume from an individual sender. To prevent spam attacks before they cause damage, the MailChannels system rate limits senders who suddenly increase their email sending volume.

The system is adaptive and there is no pre-set limit to how much email you can send in a given window of time. However as a general rule of thumb, it's good to slowly ramp the rate at which you send email in order to avoid this message. As the system notices that you are sending good email that recipients appear to like receiving, the amount that you can send will gradually increase.

Will I be billed for rate limited messages?

Yes, MailChannels charges for all message delivery attempts, even if our system chooses not to deliver the message. This policy encourages our customers to reduce abusive users within their systems, which improves our spam-fighting and leads to better email deliverability for all our customers.

What can I do if one of my users is spamming?

To avoid charges relating to users who are sending too fast, we recommend tuning your mail server configuration to reduce the rate at which queued messages are re-tried for delivery. Please follow the links below for general instructions on queue configuration for popular mail server platforms:

If you use another MTA, please consult the user manual for more information on configuring the queue retry interval.

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