mbocek@fedoraproject.org is an alias of mbocek@redhat.com in the system. You are already combined. If you email mbocek@fedoraproject.org the email should go to mbocek@redhat.com

Maybe the issue is only with the account in lists.fedoraproject.org. When I subscribe to a mailing list under one account (mbocek@fedoraproject.org), I'm not subscribed automatically under the other (mbocek@redhat.com).
It has caused me a problem already when I subscribed to epel-devel when logged in under mbocek@fedoraproject.org, then I sent an email to that list from mbocek@redhat.com and the email got rejected for the reason that I'm not subscribed.

When I log in with FAS (mbocek@fedoraproject.org):

When I log in with mbocek@redhat.com:

When I subscribe to a mailing list under one account (mbocek@fedoraproject.org), I'm not subscribed automatically under the other (mbocek@redhat.com).

That is expected, they are two different email addresses. You could have one account with multiple email addresses, one that you use for one list and another one for another list.

You could register both email to the lists you want and disable sending emails from the list to one of them. This way you can send emails to the list using both addresses, but only of them will receive the emails.

Hi. Ideally, I'd like to have just one account, with two associated email addresses. Is it possible to merge both?
Or, should I try deleting one account and associate that email address with the still existing account?

Can you try adding one of the email addresses to the other account and see if it merges the two accounts?

ie, login with fedoraproject, add your @redhat.com address and see if it merges the redhat.com account into the fedora one?

@mbocek were you able to try out @kevin 's suggestion above

@ryanlerch, @kevin,
That does not work, I remember trying it at the time of filing this issue:

@mbocek I think I fixed it, could you check please?

@abompard, yes! You're awesome, thank you.

Many thanks @abompard