Guys, before I rant I want you to know I love Thunderbird, have used it for many years. However this problem has haunted me for years and I can't believe that it is not yet fixed. This problem directly relates to problem 1048494 (when long time composing a reply Thurderbird tries to add an attachment the only given option to close or wait) - The suggestions in this post do not help. This is very easy to replicate. The problem: It is common to have embedded images in an email. (email Signatures often contain a logo). It is also common to take time to create your reply - press reply and take time to draft and create the reply. For an unknown reason - if I reply quickly, within a minute or so, it's ok. Reply sent. If I keep the reply window open for If you take longer TB pop's up "attaching" and hangs, never sends the reply. It want's to "attach" the embedded images but cant. Workaround: My workaround is either to delete the embedded images (a real pain to delete them all if it's a lot of threads in email, multiple logs in multiple signatures), or to copy text into a text editor, cancel reply, reply again and copy text back into TB and send quickly. I had this problem on TB on Ubuntu and now on Windows 7. It's nothing to do with Virus Scan (I never used that on Ubuntu). Can someone from development look into this please - It's preventing many of my colleagues using TB. There seems to be 2 problems here: 1) some timer/delay that makes TB try to 'attach' embedded images 2) the problem of replying when an email history has embedded images (p.s. I am not talking about attachments, I'm talking about embedded images often found in peoples signatures) Please TB developer community - Please take this problem seriously: Happy to send any info you want to help diagnose and resolve this? Please ask.