Tried to send an email including a 4,5MB attachment. The phone kept saying sending and after a few moments it was really hot and the battery was going low...the battery keeps going low now the moment i go online (and thus checking the email accounts). now there is no possibility of sending or receiving any email at all!

Is there a way to remove/reinstall the e-mail client?
Thank you all for your help!

Did the email send successfully or is it stuck in the outbox?
Remove your email account and add it again.

And no you cannot remove the email client.

yes the e-mail got stucked in the outbox...tried to reinstall accounts but still nothing!

Go to the outbox, hit the top bar and select "move to" and move it to the inbox or any other folder. Once the email is moved, find it and delete it.

Removing the account should clear out all folders. odd behaviour.

i forgot to remove and add again one of the accounts...all looks normal now!
thank you guys!

Actually, yes, you can. I did it once by mistake while trying to regain some rootfs space by removing additional language files - turns out the client cannot live without them. You can find modest if you select All packages (ADVANCED) in FAPman. Uninstalling it leaves the inbox intact though.