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When I email some colleagues, I get the message that their email addresses are invalid. The email addresses are not incorrect and have not changed in the years that I have worked here. They are still receiving emails to that address but I am unable to send them any. This is also the case for a few other colleagues in my department i.e., they also get the error message about some colleagues email addresses when they try and send them emails.
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Hello. This error often happens when Outlook uses old cached contact details. I would recommend removing the cached entry and selecting the colleague’s address from the Global Address List instead.
This ensures you are using the current address stored in your organization’s directory. If the email works from the Global Address List but fails with auto-complete, clearing the Outlook cache should fix it.
I deleted the contact list and re-created it and it still didn't make a difference. The frustrating thing is that after I sent the email, some of the colleagues whose emails had come up as invalid actually received the email.
Also, when I tried to send an email to just one colleague, I still had the same message pop up.
Oh, I see. thanks for clarifying. Since your colleagues still receive the emails, the addresses are valid. The error usually comes from Outlook using old cached data or a delay with the address book. I recommend checking if the same issue happens in Outlook on the web. If it only happens in desktop Outlook, clear the auto-complete cache and update Outlook to the latest version. If it still shows, your IT admin should refresh the Global Address List to make sure Outlook is in sync.
Thanks for your response. I don't use desktop Outlook, I only ever use the web version. Would you recommend that IT admin refresh the global address list, or is there anything different I should do given the issue is occurring on web Outlook?
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I think we have for very limited amount of mailboxes the same issue.
Especially when we expand a contact list from personal mailbox, the contacts show up as invalid in outlook web. Outlook Desktop doesnt have this issue.
Got it. Thanks for confirming, Kate. Since you only use Outlook on the web, clearing a local cache is not needed. If the error appears there but messages still go through, the issue is likely with your organization’s address directory. In this case, I recommend asking your IT admin to review and refresh the Global Address List in Exchange Admin Center. That ensures Outlook on the web is pulling the correct and current address data. Just let me know if the issue still persists after asking your IT.