My true IP address showing in e-mail

This is weird. My true IP address shows when sending mail via Thunderbird but not when using Outlook Express. I mean this is not the IP address that changes, but the one shown in my modem/router, which is also shown in Network Connections in XP. Why is it being shown when using Thunderbird?

 

I should have noted above that the IP address is shown when viewing full headers. Outlook Express is just showing the computer name I assigned.

 

Update:

I was told by microsoft that my computer name being shown in headers is normal for POP 3 accounts. Yahoo and Hotmail work differently and do not reveal your true IP address or computer name. So, apparently Thunderbird is just doing what comes naturally by revealing my true IP address--and I don't mean the IP address that changes.

 

Looks like you already answered your question, but it is a good idea to check the email headers for each different mail service that you use, because sometimes even webmail headers can include your ip. Sending an email to yourself is the easiest way to check.

 

I did check by using Thunderbird to send an e-mail to my Yahoo account. Seems like this is a bug in Thunderbird and nothing can be done about it. This is my real IP address (the one that never changes) being shown in headers

The moderator on the Thunderbird forum thinks this is no big deal

 

It's basically your ISP's SMTP server logging your IP and adding it to the email header. It can be used to help track down primitive spammers.
Either just use a webmail (IMAP) service that doesn't include your IP in the header, or get a privacy oriented email service that offers a SMTP server that doesn't include the IP. COTSE is good, I think FindNot also offers it.

 

There are two IP addresses being shown with one my Dynamic IP address from my ISP and the other is assisgned to me, I think, by the modem/router.