Top Deliverability’s Blog
WttW: Don’t break the (RFC) rules
- April 28, 2023
- Posted by: Top Deliverability
- Category: Industry News Word to the Wise
Word to the Wise just issued another interesting article:
It looks like Microsoft are getting pickier about email address syntax, rejecting mail that uses illegal address formats. That might be what’s causing that “550 5.6.0 CAT.InvalidContent.Exception: DataSourceOperationException, proxyAddress: prefix not supported – ; cannot handle content of message” rejection. Why do we care? It’s good to send syntactically valid email in a warm fuzzies sort of way – it shows we know what we’re doing, and aren’t dodgy spamware – but it’s increasingly important to delivery as mailbox providers are tightening up on their syntax checks. But why are mailbox providers doing that? One reason is that authentication tech like DKIM and DMARC is built around them only being applied to email. Not to messages that kinda look like email. There are ways to bypass DKIM protections by sending invalid messages. As one example, if you send multiple copies of the From: header with different values a DKIM checker
More here: Don’t break the (RFC) rules
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