If you don't have any rules (option > rules) that can do this behaviour, I suggest to see if you have a virus or trojan in your computer. Check with an online virus scaner like eset (www.eset.com - and search for online scanner)

Hello,

Thanks for suggestion. I don't have any rules a ESET works on my PC.

Possibly something is still in the temporary cache.

When you create an email and add an attachment and send, a temporary cache is created and after it has been sent, the temp cache should be deleted. But I'm wondering if something has been left in the temp folder and wrongly attached.

I created an email and added an image attachment. These files were created in UserName/ AppData > Local > Temp

• nsemail.eml
• nsemail.html
• nsemail.tmp

After sending they had gone.

Please check you do not have something lurking in the Temp file.

Also, do not scan outgoing emails just in case the Anti-Virus is messing up things.

Could you also do the following and then report back on results:

Make a backup of profile folder name and save on desktop or external device.

• http://kb.mozillazine.org/Profile_backup

Please make sure Anti-Virus is not scanning Thunderbird folders on startup nor when receiving/sending email.

In Thunderbird

• File > Compact Folders

this removes all traces of marked as deleted emails.

then for each folder do this:

• Right click on folder and select 'Properties'
• click on 'Repair folder' button
• click on ok

this repairs the .msf indexing file

After compacting and repairing index files: Help > Troubleshooting Information click on 'show folder' button a new window opens showing contents of profile name folder.

Close Thunderbird now - this is important

Look for and delete this file:

• panacea.dat

Restart Thunderbird.

do a test email to yourself or another of your email addresses using the same email as before and report as to whether it attached the unwanted attachment.

Confirm: do you use imap or pop mail accounts or both? Is the problem in a pop or imap mail account?

Hello, Toad-Hall

I have pop3 mail account. I have checked and there are no such files (semail.*) into UserName/ AppData > Local > Temp. I have executed Your instructions about Compact/Rapair folders (mainly I use virtual folders) and the same incoming email with attached images. The issue with email with unwanted attachment don't arose. I will observe the issue some time (as it arise occasionally) and post the result.

Thanks for Your advices!

I was observing the issue some time and it never occurred. Thus it can be assumed that Toad-Hall provided right solution for my issue.