What came in an amphora's neck and around it, perhaps, as a seal and guard against leaking was often flaxen tow known as "stuppa" to Romans of the ancient world.
Incidentally, stuppae's function as stoppers, many argue, is where the English word "to stop" has its origin. You do not need flax or oakum, though, to seal your IMAP email account at the right time and prevent too much mail from leaking into Mozilla Thunderbird:
›› Wish Mozilla Thunderbird would not keep copies of all your emails offline on your computer when it is already stored quite safely on the IMAP server? Here's how to set up Mozilla Thunderbird to store only the most recent messages locally.