The wife of a friend of mine had a problem. Sending emails from her iPad would change the sender from something like "wife<wife@owndomain.dk>" to something like: "wife<husband@gmail.com>". This was of course frustrating like hell, as responses to her emails were sent to her husband, even though the recipients saw her name in the email applications. She had no problems with sending correctly from her Mac or iPhone. They had already checked the SMTP-address - repeatedly - so it was a mystery.
To fix this, I checked the SMTP-server list, i.e. Outgoing mail servers. There were a number of servers listed, as the iPad had belonged to the husband, but the correct SMTP-server of the "wife@owndomain.dk" was present. Also present was a Gmail-SMTP-entry, with the husbands login credentials.
The culprit was that there was no password for the login credentials for the correct SMTP-server, so we set that, and removed the gmail-entries. This resolved the issue. The last part was not necessary, but just to be sure the problem will not come again.
My analysis is that the original SMTP-server somehow was unavailable and that Mail on the iPad had (wrongly) asked for the correct password instead of recognizing the offline situation. Handling this error, the wife had somehow deleted the password. Doing this is too easy, Apple! Then the failover for Mail was of course to take the next SMTP-server on the list, and here Gmail does something very strange. It leaves the name of the sender "Wife" but changes the email-address to be the one of the account sending it, so wife@owndomain.dk becomes wife<husband@gmail.com>. Not smart either.
The fix worked, btw.