In point of fact, at the time the delay problem appeared, I was still using the Comcast POP server, and I switched to IMAP at Comcast's recommendation, only to have the same problem, which turns out to have been initiated by the upgrade of my Thunderbird to v60.3 .
If you don't have this delay, you may still be using an earlier version of Thunderbird, in whihc case, don't do the v60 update.
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For a few weeks we have had a similar email download problem, with the Comcast imap server having devolved from instant response to one taking about 25 sec each time it was polled. I too thought that this was a Comcast problem, but it turns out that the fault is with Mozilla Thunderbird.
Within the last few weeks, Thunderbird on both computers has been upgraded to version 60.3.2, in which the default connection protocol was secretly "upgraded" from IPv4 to IPv6, which the Comcast imap server does not recognize. As a result, Thunderbird tries and tries to make the connection with IPv6, sometimes taking over 25 seconds, before dropping down to v4, and picking up the email. The details of the problem are discussed here:
Of the several solutions offered, I chose the simplest, namely disabling IPv6 on Thunderbird, thereby forcing the connection to IPv4, and restoring my client to an instant connection with imap.comcast.net. If you use the Thunderbird client with several servers, you might choose to try the second method, just forcing theIPv4 use on specific server, and not on others.
Here's how: in Thunderbird, goto Tools>Options. On the Options screen, select "advanced" tab > "General" subtab, and in the lower right corner find the button "Config Editor" Click on it, acknowledge the warning, and scroll a long ways down to:
network.dns.disableIPv6 boolean (default: false) Double-clikc on the line, and the value will change to "true" Back out and Okay, shut down and restart Thunderbird, and your client will connect to the imap server in a flash.
This concept may be applicable to other clients, and likely with Cocast's POP server as well.
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