Problem attaching some emails

We’re using this version of the CRM:
Version 7.4
Sugar Version 6.5.20 (Build 1001)

I don’t know which version of the Outlook Plugin I’m using, sorry.

I attach emails regularly to the contacts in the CRM thanks to the Outlook plugin, but sometimes, I can’t, the plugin says “no result” when looking for the email address.
I check if the email address is correct in the CRM, and it is.
Nevertheless, I add the email address looked for in the plugin to the contact, I set it as “primary”, I save the change, but when I try again the result is the same “no result”.
What is strange is that when I remove the other email address and save the change, both addresses still appear in the contact.
I have to remove both addresses so that only one appears in the contact when saving the change.
I really can’t think of what the problem could be.
Can you help?
Kind regards,