larieu
I have tried that but from my knowledge if the default setting of "show only last 30 days" is overpassed the phone will not take into account older emails
And this is a "user side" setting (not all users will do it, and definitely users which don't care will take no action)
This is nothing to do with how many messages to display. This relates to the purging of messages after deletion.
ie
In iPhone parlance, "how many days after a message is deleted before the message is removed (purged) from the nominated folder".
I edited my original post with more info re where to configure this on iPhones (models 3 & 5 which I have), maybe read it again.
"Settings, Mail, select account, Advanced, Deleted Messages - Remove (or similar), choose Never, One day, One week, One month,
Remember to save when exiting (select Done I think)."
Users who do not care to do it will reach their quota and then when they complain, tell them to change the settings to purge the deleted messages after say, one day.
It's a simple setting change that takes under 1 minute to do !
How you resolve your problem is your choice.
I was just correcting your statement that there was no apparent place on mobile phones to set the purge time, well there is, at least on iPhones.