Don’t break the (RFC) rules

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...


I just added a DMARC validation tool over on tools.wordtothewise.com. You can give it a domain – such as ebay.com – and it will fetch the DMARC record, then explain and validate it. Or you can paste the DMARC record you’re planning to publish into it,  to validate it before you go live. If you’ve not seen our tools page before, take a look. As well as DMARC we have a DKIM...

The twilight of /8s

A “/8” is a block of 16,777,214 usable IP addresses. That’s a big fraction of the entire IPv4 address space – about 1/224, in fact. Each one is all the addresses that begin with a given number: is all the IP addresses that begin with “10.”, “” (or “184/8” for short) is all the IP addresses that begin with “184...

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