I have a mail server that periodically connects to the Internet via modem dialup. And before I was able to send emails with attachments of 300kb and 500kb in just only 1 or 2 minutes. I have not made any change in Postfix and now it takes longer than normal to flush the Postfix queue. Sometimes it takes more than 10 minutes to deliver an email of just 300kb. If this mail is in queue with others mails containing only text, then the rest will be delivered normally while the one containing an attachment of 300kb is delayed more than usual. Previously this was not happening and all the emails have been sent very quickly.
Any suggestion of what is going on here? Can this be caused by a very large Postfix maillog file that needs to be rotated, or reconfiguration the