What you’re seeing
- Replies to older messages bounce, and the bounce shows a long address beginning with IMCEAEX.
- Picking a colleague's name from Outlook's autocomplete list produces a bounce, while typing the full address works.
- Meeting updates and calendar replies to people who were moved fail with the same style of address.
- The bounces began right after moving mailboxes to Microsoft 365 or a new Exchange organization.
Common causes
Every environment is different, but these are the causes our engineers find most often:
- Outlook's autocomplete cache stores the internal Exchange address from the old system rather than the SMTP address.
- The migrated mailboxes are missing the old internal address, so the new system can't match it to the right person.
- Older messages and calendar items still reference the previous organization's internal addressing.
- A cross-tenant or third-party migration tool did not carry over the legacy address attributes during the move.
Why it matters
After a migration, staff naturally reply to existing threads and rely on autocomplete. When those replies bounce, colleagues and teams miss messages, meeting changes don't reach attendees, and people lose confidence in the new system. The problem affects internal collaboration most, and because the error text is cryptic, users often assume the new mail platform is unreliable rather than recognizing a fixable leftover from the move.
How AskTechGurus fixes it
Skip the trial and error. A certified engineer works on your actual system, finds the root cause, and fixes it properly.
Tell us what’s happening
Submit a ticket in about two minutes. Paste the error, describe what changed, and pick your tier. No charge to submit.
A certified engineer diagnoses it
A vetted, US-based systems engineer claims your ticket, usually within minutes during business hours, and investigates over a secure remote session you can watch and end at any time.
Fixed and verified with you
The engineer resolves the root cause and confirms with you that it’s working. You don’t just get a workaround, and you get a plain-English summary of what was wrong.
Pay only when it’s resolved
Fixed price from $99, invoiced only after you approve the fix. If it isn’t resolved, you don’t pay.
Frequently asked questions
Does every user need to clear their autocomplete?
Not always. Fixing the address records on the mailboxes themselves usually resolves the bounces for everyone at once, and our engineer confirms that approach first.
Were any messages lost?
Bounced messages go back to the sender rather than disappearing, so nothing is lost silently. Anything important that bounced can simply be resent once the addressing is corrected.