In Sophos Secure E-Mail you can set how long back e-mails should be synchronized. There is a choice:
• 1 day
• 3 days
• 1 week
• 2 weeks
• 1 month
• All

For some users, 1 month is too short, but All makes a very large local SSE database, which leads to problems with the app.

My suggestion would be to delete the selection 3 days and 2 weeks and instead take 3 months and 6 months.
If that is not technically possible, at least the choice of 3 months would be very helpful.