I've blogged about this before, covering the different types of NDRs (non-delivery reports, aka bounces or rejections) that you receive back when trying to send email messages to email addresses that are invalid; either never having anyone home, or now no longer being a valid mailbox. Find that here.
But this time around, allow me to get more specific. I run an email newsletter, right? It’s not huge, about 1400 people, but a fair number of subscribers use Microsoft 365 for corporate email hosting. People move on to other companies, leaving their current job and current work email address behind. When that happens; guess what the SMTP rejection is that I receive, when a Microsoft-hosted mailbox is no longer valid? Yup, it’s “550 5.4.1 Recipient address rejected: Access denied.” Seemingly every time.
This Microsoft support page hints at this being a response for invalid addresses; see how it suggests that you first check to see if you spelled the user’s email address correctly? There are also potentially other reasons this rejection can occur, from a misconfigured M365 environment to a block against the sender; but this is likely to be rare, especially the latter, if you’re a good sender and not shoveling spam to somebody to the point where they’re annoyed enough with you to manually implement a block against your mail.
It’s a confusing one, for sure! Even though it specifically says “access denied,” as I explain above, it’s actually most often a user unknown/nobody home bounce, and I would generally treat it as such. I figured this would be a good thing to get out there to help folks be able to tune their bounce handling and/or review rejections more accurately in the future. Good luck, and be sure to check out my 2023 blog post with more types of Microsoft user unknown SMTP rejection codes.
I've blogged about this before, covering the different types of NDRs (non-delivery reports, aka bounces or rejections) that you receive back when trying to send email messages to email addresses that are invalid; either never having anyone home, or now no longer being a valid mailbox. Find that here.
But this time around, allow me to get more specific. I run an email newsletter, right? It’s not huge, about 1400 people, but a fair number of subscribers use Microsoft 365 for corporate email hosting. People move on to other companies, leaving their current job and current work email address behind. When that happens; guess what the SMTP rejection is that I receive, when a Microsoft-hosted mailbox is no longer valid? Yup, it’s “550 5.4.1 Recipient address rejected: Access denied.” Seemingly every time.
This Microsoft support page hints at this being a response for invalid addresses; see how it suggests that you first check to see if you spelled the user’s email address correctly? There are also potentially other reasons this rejection can occur, from a misconfigured M365 environment to a block against the sender; but this is likely to be rare, especially the latter, if you’re a good sender and not shoveling spam to somebody to the point where they’re annoyed enough with you to manually implement a block against your mail.
It’s a confusing one, for sure! Even though it specifically says “access denied,” as I explain above, it’s actually most often a user unknown/nobody home bounce, and I would generally treat it as such. I figured this would be a good thing to get out there to help folks be able to tune their bounce handling and/or review rejections more accurately in the future. Good luck, and be sure to check out my 2023 blog post with more types of Microsoft user unknown SMTP rejection codes.
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