Hi. Sounds like a setting with the email accounts: Are they POP, IMAP, Exchange...? Play with the settings again - follow this Mail Assistant article for iPad: http://www.apple.com/support/ipad/assistant/mail/#section_0
good luck :-)
Hey! Thanks so much for your help!
I checked the settings, it is POP - but it didn't help playing with the settings.
But, the Mail Assistant article for iPad that you gave me really did help! They suggested to re-start my iPad (pressing the on/off button, and the button which closes applications at the same time for 10 seconds, until I saw the Apple appear). This has really helped! It feels so good to be able to send messages again!
Thanks for taking the time to help me, I really appreciate it!