I recently encountered a rather nasty and time consuming issue regarding my hosted mail servers. The problem showed up when the regularly timed, automatic accessing to my (personal domain) mail servers would seemingly fail at times. No other error–my email was just not getting through at times. I knew something was wrong. This precipitated many hours of troubleshooting to get to to the root of the problem.
It was caused by comodo’s dns server blacklisting my isp (aplus.net) where my mail servers resolve to. Very insidious. The complicating factor to determine what was happening is that it appears that the comodo’s dns server has some sort of timeout feature. At times I could reach my mail servers’ dashboard and at times I couldn’t. Believe me, it took me awhile to get to the bottom of this as it didn’t occur to me that it was comodo’s dns server doing this–it had been so long ago that when first installed it.
So beware, there’s no indication to the user if just the isp is used for hosting mail and no web access. Making it even worse, is that it was intermittent (i.e., some sort of timeout involved.)
When comodo blacklists a rather large isp, there are a lot of unintended consequences. I reported the problem both to aplus.net and comodo. After a couple days, aplus.net support says the problem has been fixed. Webinspector no longer lists it as being blacklisted. However, I have no idea if or when comodo’s dns has been updated to reflect this. I can’t “test” it reliably because of the randomness of it. I will no longer use their server (thanks anyway) until they start publishing exactly which sites are currently being blacklisted–I’m unwilling to just use a trial and error method–email delivery is too important these days.