Try telling your antivirus to leave you email alone. I bet things load better then.

Airmail said

Try telling your antivirus to leave you email alone. I bet things load better then.

I'm using Microsoft Security Essentials and as far as I can tell it does not scan incoming email.

I found this article stating is does scan downloaded files and attachments. I do not use this software so I cannot help you much there.

http://answers.microsoft.com/en-us/protect/forum/mse-protect_scanning/does-mse-scan-e-mail/2b9dd412-1116-4d28-84bb-ebeab5d28ced?auth=1

Airmail said

I found this article stating is does scan downloaded files and attachments. I do not use this software so I cannot help you much there. http://answers.microsoft.com/en-us/protect/forum/mse-protect_scanning/does-mse-scan-e-mail/2b9dd412-1116-4d28-84bb-ebeab5d28ced?auth=1

That article has some conflicting statements; the only thing that may affect email that I see is Real-time protection. I will turn it off and have someone re send one of the large emails as a test.

Thunderbird is probably unable to complete the download and therefore cannot sign it off as completed, so tries again next time. This could well be related to AV scanning impeding the normal flow of data, but it can happen simply because there's something amiss with the structure of the message.

If you do already have a usable copy of it, then you could go to your provider's webmail portal and delete the message there, since it is unlikely to ever successfully download to Thunderbird's satisfaction.

Zenos said

Thunderbird is probably unable to complete the download and therefore cannot sign it off as completed, so tries again next time. This could well be related to AV scanning impeding the normal flow of data, but it can happen simply because there's something amiss with the structure of the message. If you do already have a usable copy of it, then you could go to your provider's webmail portal and delete the message there, since it is unlikely to ever successfully download to Thunderbird's satisfaction.

Turned off Real-time protection and multiple downloads are still occurring. I have been deleting the messages from my webmail to stop the multiple downloads; if this problem can't be solved I will look into other email programs.

I just tested sending myself large files. I started with a 36 meg raw image file and my provider, Comcast, rejected it as too large. Then I tried a 24 meg image file with the same result. I moved down to a 14 meg image file and it sent from one of my accounts with Comcast to another with the same provider and was delivered just fine and only once.

Feel free to use another email client and report those results.

I tried another email program and it did not download multiple copies. Tried uninstalling TB again and deleted the profile before re installing and still had same problem. Sent one of the large files to my friend who I had installed TB on his computer for him and he did not have the problem. So I changed my email from POP3 to IMAP and now it appears that the multiple download problem has gone away. I wish I knew why I had a problem and my friend (and others) did not.