Basically, they should first make sure that no longer needed emails are moved from the mailbox. Please also consider the recycle bin here. The procedure for cleaning up differs between the various email clients (Outlook, Apple Mail, etc.) only in the handling. E-mail clients usually offer archiving functions that allow e-mails to be saved locally for specific purposes. It is advisable to check whether you need to have e-mails with large attachments or old e-mails permanently available. Archiving or storing large attachments locally relieves the load on your mailbox on the server side and thus increases performance.