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Deliverability Blues 2013
We recently had a rash of spam sending due to someone finding, guessing, or leaking a user's password. Sometimes, it just requires that, not some security breach. Well, we didn't catch it and stop it in time, and now we're suffering some deliverability problems ranging from slowdowns to outright blocking by some servers.
What I've learned, aside from the importance of being proactive, and maybe even running spamassassin on outgoing mail, is that a few email providers are clamping down on spam by blocking servers, or downgrading the deliverability of some servers.
Some of these companies are Gmail, Yahoo, AOL and Microsoft. These companies dominate the web-based email, and represent the majority of email on the network.
I don't know the details, but there are a number of things which help deliverability, ranging from easy to hard, cheap to expensive. This article will be revised with things I'm doing to improve deliverability. In no particular order.
Sender Policy Framework (SPF)
example.com. IN TXT "v=spf1 a mx ~all"
And how it looks in djbdns/tinydns:
'example.com:v=spf1 a mx ~all:::
In tinydns, you need to escape the : with \072 (octal 072), because : is a delimiter.
'example.com:v=spf1 a mx ip4\0718.104.22.168 ~all:::
Test Outgoing Mail
Inbound Email Issues