@Victor Ivanidze, this is only true if you have a single Exchange connection. With only one server, selections from the "Other Email Address..." selection generally (not always) do stay in the From drop-down. However, once you add a second server, then future selections from the Other Email Address never add to the drop-down. Is there a way to force them to "stick" and appear in the drop-down in the future?
In this case, you can see 3 servers above the block horizontal line in the drop-down plus 3 additional From options below that line. It is impossible, as far as I can tell so far, to add any more now because there is more than 1 server in the top block:
I have tried searching the Registry and "%localdata%\Microsoft\Outlook" but have not been able to find where these values in the drop-down list are stored to add to it.
The only work-around I know of is to delete the Outlook profile, add the first server, use all the From addresses so they populate the drop-down list, then and only then, add the other servers. BUT, this won't help if you need to add From addresses from multiple host servers.