Get Mail greyed out at startup

[loninappleton]

Hello

I am on Thunderbird 91.
I have set Tbird to Get Mail on startup and Leave Mail On Server. Both options
register without error.

When the program starts, "Done" is visible lower left screen and Get Mail
top left is greyed out. I get the new mail by then clicking on Get Mail top left
and the mail is retrieved from the ISP.

And older Thunderbird 78 not upgraded on a separate PC does not have the
problem. What do I need to do?

[DanRaisch]

I am on Thunderbird 91.
I have set Tbird to Get Mail on startup and Leave Mail On Server. Both options
register without error.

Have you confirmed that in addition to "Check for new messages at startup" you also have "Automatically download new messages" selected?