Why is Yahoo/AOL throttling my email and returning a 552 error?

Email marketer from EmailOnAcid discusses the importance of maintaining a clean email list. Sending to old/unengaged email addresses can negatively effect sending reputation and increase the likelihood of throttling and being marked as spam.

Email marketer from Mailjet explains that Yahoo and AOL require email senders to authenticate their email addresses with SPF, DKIM, and DMARC; maintain a spam complaint rate below 0.3%; and provide one-click unsubscribe options for recipients. Not meeting these requirements may result in email throttling or blocking.

Email marketer from Neil Patel's Blog discusses factors impacting email deliverability, including sender reputation, authentication (SPF, DKIM, DMARC), and engagement. Poor sender reputation can lead to throttling or blocking by ISPs like Yahoo/AOL.

Email marketer from Email Geeks shares that they are seeing a handful of similar errors, but at extremely low rates, like 1 per 500k transmissions.

Email marketer from Gmass says email providers like Google, Microsoft, Yahoo, and AOL implement throttling as a mechanism to limit the rate at which emails are sent from a particular source. This can be the result of multiple reasons. Gmass details 7 reasons for this, including: Sending Too Many Emails Too Quickly, Poor Sending Reputation, Low Engagement Rates, Content Filters, Inaccurate Email List, Technical Issues, and Shared IP Address

Email marketer from StackOverflow shares that the error 552 indicates the user has exceeded their quota, therefore the email cannot be delivered.

Email marketer from Reddit suggests that Yahoo/AOL throttling might be due to sudden spikes in email volume, especially if sender reputation isn't well-established. They recommend gradually increasing sending volume to build trust.

Expert from Word to the Wise, Laura Atkins, explains that senders who are being rate limited or throttled by mail systems need to investigate the reasons behind the traffic shaping, by finding out from the mail system itself. These can include volume spikes, complaints, and the quality of your traffic.

Expert from Spamresource.com explains that Yahoo and AOL now require, at minimum, that you authenticate your mail using SPF and DKIM. If they can't verify you're authorized to send mail for your domain, they're more likely to throttle you, reject your mail, or send it to the spam folder.

Expert from Email Geeks suggests that the issue might be related to the server doing something slightly unusual that Yahoo previously accepted but is no longer okay as they prepare for new 5321 and 5322 enforcement, and asks what command triggered the 552 error.

Documentation from Mxtoolbox defines that throttling is when a mail server temporarily rejects messages from a specific IP address or domain if it detects a high volume of emails, or suspicious activity, originating from that source.

Documentation from RFC Editor explains that a 552 error, specifically '5.2.2 Quota exceeded', indicates that the recipient's mailbox has exceeded its storage limit. This is a permanent failure.

Documentation from Google Workspace explains that Google applies rate limits to prevent abuse and maintain system stability. Exceeding these limits can result in temporary throttling or rejection of emails.

Documentation from Postmark explains that a 5xx error is permanent. 552 means 'The email account is over quota' - there is no action you can take.