You need to set-up your account as IMAP.

My incoming server setting is imap.windstream.net with port 143. My outgoing setting is smtp.windstream.net with port 25. Both settings are the same as the ones on my phone which seems to work fine.

Thunderbird does not seem to affect my webmail. So, now, messages I delete on Thunderbird still show up on my phone. If I delete them on my phone first, they do not appear on my desktop Thunderbird.

Is there more to setting-up my account as IMAP than what I described above?

Try to compact folders after deleting a message in Thunderbird. It seems folders on the IMAP server are not refreshed to indicate message deletions until the local folder is compacted.

http://kb.mozillazine.org/Compacting_folders

Hello Christ1:

Compacting seems to work. Now, the next logical question is why do I have to do it with Thunderbird and not on my phone? I never had to do it with Outlook either.

Is there a way to get Thunderbird to compact folders automatically? I read (skimmed) the Mozillazine article and I gathered that is a future improvement. Any insight?

Thanks, by the way.

why do I have to do it with Thunderbird and not on my phone?

I don't know.

Is there a way to get Thunderbird to compact folders automatically?

Yes, you can set a threshold when compacting is triggered. It's all described in the article.

I gathered that is a future improvement.

I don't know what you're talking about.