Do you try to restore access immediately by removig IP from the fail2ban ban list? or restart the jail?

Not yet. It happens sometimes. I am waiting it now ))

2 - It's not an ideal solution to ignore someone, but if necessary, you can add ignoreip = 10.10.10.10 to the jail configuration.
Alternatively, you can increase maxretry to a higher value, such as maxretry = 10.
Check your jails in the /etc/fail2ban/jail.d/ directory.

Or you can add an ignoreregex to the filter — something like:
ignoreregex = connect from unknown\[172\.20\.20\.20\].*$

We have an internal corporate network with a fixed external ip address. When someone makes a mistake entering their username and password, iredmail blocks the entire network and we cannot access our mail for several hours.

1) Please tell me in the documentation where and how can I immediately restore access to mail?

2) Is it possible to make this blocking not work at all for certain ip addresses?