What you’re seeing
- A newly set primary reply address reverts to the old one after a few hours or overnight.
- The Microsoft 365 admin center grays out the address field or says the object is managed on-premises.
- Recipients still see replies coming from the old address or old domain.
- A distribution group keeps sending as its original address after a rebrand.
Common causes
Every environment is different, but these are the causes our engineers find most often:
- An email address policy applies to the mailbox or group and stamps its own primary address over any manual change.
- The object is synchronized from on-premises Active Directory, which is the source of authority, so cloud edits are rejected or overwritten.
- The on-premises proxy address list still marks the old address as primary, and the next sync cycle restores it.
- The new address uses a domain that has not been verified in Microsoft 365, so directory sync drops or rejects it.
- The last Exchange server was removed from the on-premises environment, leaving no supported tool to manage the address there.
Why it matters
The primary address is what customers see on every reply, so getting it wrong undermines rebrands, mergers and name changes. Staff appear to be emailing from a retired brand or an outgoing employee's name, and some customers start replying to addresses that may later be removed. When changes keep reverting, administrators lose time repeating the same edit, and attempts to force it can break the sync relationship for that account, causing duplicate or orphaned objects.
How AskTechGurus fixes it
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Tell us what’s happening
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A certified engineer diagnoses it
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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
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Frequently asked questions
Will people still be able to reach the old address?
Yes, if it is kept as a secondary address. Mail sent to it continues to arrive in the same mailbox, while replies go out from the new primary address.
Does changing the email address change how the user signs in?
Not necessarily. The sign-in name is a separate setting, although many organizations keep the two matched. We confirm with you whether the sign-in name should change too before touching anything.