Have been using Word mail merge with Outlook for a long time without problems.
I recently change job, added a new e-mail address to Outlook and started mail merging from this new address.

I wanted to keep the previous account for addresses and references. So as an archive so to speak, without using this account to actively send e-mail.

Last December I upgraded to Windows 10 and lost Outlook completely. The easiest way was to re-install Outlook . I managed to get it all up and running again, including the mail merge feature.

Yesterday I added my old e-mail account again and to my surprise mail merge is suddenly using this old (unused) e-mail address!
I had these addresses in Outlook before and it always used the correct e-mail address. Now it is using my old address which I do not want.

I am reading possible solutions by adding a new profile but in that case I do not have the old and new account in Outlook. It has worked for months with all my accounts in one profile.

Is there any way to fix the correct e-mail address for mail merge, even with more
e-mail addresses in my outlook profile?