Hi all,
Case solved.
On my iPhone 4 under IOS 7.2 (highest poss. ) I had 10 POP3 accounts. Each 3 months my Mail Usage would run upto 800 MB to 1 GB...!
A persistent Apple bug caused any attachment to reside in storage even when the original email was deleted.
Since thevrmailclient itself cannot be deleted (yes under IOS10 it can) only the following proved successful.
Per account save any text or leftover attachment.
Then delete each POP3 account.
Observe in Usage your MB's go down!
In my case when 10 POP3 accounts were deleted Mail Usage went down from some 800 MB to some 70 MB.
I would have. a list ready of all usernames and passwords and the whole operation tolk me under 1 hour per quarter.
As I observed that IMAP accounts do not suffer from this effect so I changed all of them into IMAP.
Now my quarterly storage/usage buildup is only some 150 MB. So POP3 is the culprit combined with bad Apple internals.
A similar bug exists in SMS where the attachments will not be deleted with the messages but accumulate.
There is a Windosbased app to clear those out. Ask me for its funny name if you're interested.
Maria