How can I tell if my email has been blocked?

The root problem is that there are simply so many reasons your mail may not get through these days that it's practically impossible to determine which reason is contributing to your situation. On top of that it could be a combination of reasons.

Here are just a few reasons that your email may get to some people, but not all...

• The recipient you're having problems with may have a particularly aggressive spam filter, and your mail may be getting filtered as spam based on its content. Make sure that the message you send is totally benign from a spam perspective - no words or phrases that would possibly trigger a spam filter.

• The recipient you're having problems with may have a particularly aggressive spam filter, and your mail may be getting filtered as spam because of configuration issue with your email. The most common scenario involves sending "From:" one address using the services of another ISP. For example if I were to send "From:" some email@ask-leo.com, but us the mail servers of my ISP, "covad.net" to do it. In theory it's legitimate, but it's also one of the ways that spam works and thus subject to some extra scrutiny.

• Yes, your IP could be on a blacklist somewhere. If your IP address has been known to send large amounts of spam it could have been blacklisted by one or more of the blacklisting services, and your recipient's mail provider may use that service to block spam.

• It could also be the IP address of your mail provider that's causing a problem. When you send email it's first sent to your email provider's server, and from there it gets sent on to its final destination. If your email provider has been seen as a source of spam in the past then it's IP address or address ranges could appear on a blacklist. Once again, your recipient's mail provider might use a service providing that blacklist to block spam.

• Your recipient's email program might be at fault: it could decide that your email is spam for any number of reasons, and discard your email.

In all the cases above, when your email gets filtered as spam there's no guarantee that you'll be notified. There's not even any guarantee that your recipient will even get the chance to see your email in a spam folder. Quite frequently the email is simply discarded.

While spam is the biggest reason your mail might not make it through, there are others:

• Your recipient's email program might be misconfigured - particularly if they use "inbox rules" to automatically organize email.

• Your recipient might simply have deleted the email.

• And yes, lastly, your recipient might have blocked you somehow.

There's no guarantee that you'll get any kind of notification. In fact, it's most likely that you will not.

And to top it all of, as I've written about before, there's no reliable way to track if email has been opened or deleted.

If you find yourself in this situation, you can certainly ask your recipient to "whitelist" you, which may bypass some of the possibilities I've mentioned above. But ultimately I would try using a different email account via a different provider to try communicating with whomever it is you're having troubles with.