There are a few suggestion here if you use VZ webmail.http://www.verizon.com/Support/Residential/Internet/highspeed/email/storage/questionsone/128012.htm Also - SEttings - general settings - display - number of messages per page - Default is 20, mine is set for no limit
How do I increase the number of emails stored in my inbox. Now, the old ones are deleted automatically after about 20 are in the inbox.
Verizon doesn't autmatically delete messages.
Any time mail disappears from the server, there's a pretty good chance there's some device pulling it off. This can happen even without you intending it to. For example, the default Verizon setup for a long time (and possibly still) configured Outlook automatically unless you were paying attention and unchecked the box during the install.
The easiest way to fix it is to change your password. Once the device(s) can no longer authenticate, the disappearances should stop.