If you’re using POP3 mail configured on Outlook and you come across an issue where large emails remain in the outbox for a minute and then timeout, you may want to increase the server timeout limit. The default limit is 1 minute.
1) Click tools
2) Click email accounts
3) Click the pop3 account and click change
4) Click more settings
5) Click advanced
6) Increase server timeouts as you wish and apply settings.