Right-click the folder, Properties, and look at the Retention Policy tab. If you don't wish to retain mail older than 90 days, that can be done for a particular folder. But if you want to keep the older sent mail and sync just the last 90 days, I think you would have to create a filter that moves mail out of the Sent folder when it's older than 90 days.

sfsfhowes said

Right-click the folder, Properties, and look at the Retention Policy tab. If you don't wish to retain mail older than 90 days, that can be done for a particular folder. But if you want to keep the older sent mail and sync just the last 90 days, I think you would have to create a filter that moves mail out of the Sent folder when it's older than 90 days.

What does "retain" mean.

To be clear, I don't want to delete any emails unless I manually click Delete on some email.

Retain means keep, i.e. do not delete. Since it's not possible to sync on a per folder basis, it appears you would have to use a filter. Or, access the account through webmail, move the old sent mail to another folder, then in TB uncheck that folder in the Subscribe settings (right-click the account in the Folder Pane, Subscribe...). In that case, depending on the mail provider, you might be able to set up the filter on the webmail site so the process is done automatically.

hi sfhowes,

not sure i want to move Gmail's Sent Mail to another folder. I actually don't think you do such a move. You can only add a label to Sent Mail.

My provider is Gmail.com. It's a gmail.com email address. I usually use Firefox browser to access gmail.com. I'm just seeing if Thunderbird can help me when I'm offline. But if it doesn't work with TB, I can just stick to accessing Gmail through Firefox.