Just wrote a long PM on my i-phone and login was timed out. Was told to login again, did and now I can`t find the PM to send it, UGH. Thinking next time I should save it to draft if I suspect login expired. Sure doesn`t  help me now.
Any info appreciated

Start composing PM.
After a few minutes, send to yourself.
Open the New Mail.  
Choose Action, Forward.
Revise your PM.
After a few minutes, either send to yourself OR recipient.
If sent to self: open, forward, revise, repeat.
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OR
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TER could have installed open source Forum Software with a built-in fully functioning private messaging system that saves your work after incremental changes in the event of a crash or timeout and you wouldn't have this problem.

When it's ready. I prefer typing in that app to the PM form anyway. Or just get in the habit of copying to the clipboard just before hitting send/submit. Kind of a good habit when typing about anything online, just in case. If all goes well, you never need to paste it anywhere, but at least you have it.

Was added with the new TER.

All the other advice here also works, but here is another one and it's what I do now after losing a few. When you hit send and it tells you to log in, hit the back button. Once you login this doesn't work but if you immediately hit back, Your messsge should still be there. It's offline so you can't send it but you can copy it, then log in, go back to your message and paste it and hit send. Or copy it and paste it into notes, then retrieve it from notes later to paste into the PM.  

I usually write a message in a separate tab. I've I've been at it for awhile, I'll go back to another tab and refresh it to make sure I'm still logged in, this way I have a chance to re-login before I send the message.

I think that TER's Draft feature isn't very sophisticated. Write. Save draft. Open draft puts you back in the regular editing window so if you crash or get disconnected, you lose your efforts. There is no SAVED draft once it is opened in the mail editor.  
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When you send to yourself, open, forward ... the last sent version will always be retained in your Inbox.  
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A modern mail system (e.g., gmail), saves your edits on the fly. In the event of a crash or disconnect, your work is automatically saved as a draft and you lose a few keystrokes or, at most, a few sentences.

Usually what happens is I will get a phone call in the middle of typing a post or PM, by the time I get off the call and remember to finish my message/post I've been logged off. When this happens I do the same as you, I simply copy it, log back in, and then paste it after logging back in. It's not a problem I ever felt the need to bother admin about. It's hardly unique to TER.

quite often when I'm distracted or writing a well thought out response to the dipshits on the P&R board. Lol. Remember to copy your message and simply paste it back if you have been inactive for awhile.