What emails systems are you using as they all have a difference method you just have to search the tools setting or the account setting I only use Thunderbird Email
In Thunderbird Click Tools-Account Setting-expand the ISP name- Server Setting
And you see Leave message on server and the amount of days 2-60?
What it means is that all your messages will be stored for the time you set
If you only use 1 pc and check you mail on a daily basic you can set it for 2 days after that it is deleted automatic by the server
So if you go on holiday for 10 days an can not check your mail on a daily basic,
You will lose 8 days of mail, as the mail server will delete mail older than 2 days