How to Change the Email Domain of Every Address in a List After a Rebrand

To change the domain of every address in a list, write one line per change, old domain then new domain, and replace the text after the @ in every matching address. The email domain replacer does this in your browser: the part before the @ is never touched, other domains are left alone, and every change is listed so you can review it.

The swap is the easy half. The risky half is whether the new addresses exist.

When a swap is the right fix

A company that rebrands, merges or moves from .co to .com often moves its mailboxes to the new domain and keeps the names. A list written before that date still holds the old domains. The swap turns jane@old-company.com into jane@new-company.com in one pass. For why mail starts bouncing after a move, see cold email bounces after a domain migration.

Step 1: do it by hand

For one domain, use find and replace on @old-company.com with @new-company.com. Including the @ stops it from also matching not-old-company.com, but it still misses subdomains such as mail.old-company.com, and capitals such as @Old-Company.com depend on the program's case setting. With several domains, you repeat it for each and have no list of what changed.

Step 2: use the replacer

1. Upload the CSV or .xlsx, or paste the cells with the header row first.
2. Pick the email column and write each change on its own line, old domain, arrow, new domain.
3. Decide whether subdomains such as mail.old-company.com change too.
4. Check the list of changed addresses and download the file.

A domain matches when the whole text after the @ equals the old domain, in any mix of capitals. Domain names are not case sensitive, and the new domain is written in lower case. With subdomains on, mail.old-company.com becomes mail.new-company.com. When two lines could both apply, the exact match wins, then the longest parent domain.

Leave the mailbox name alone

The part before the @ is copied exactly, capitals included. RFC 5321 allows a server to treat it as case sensitive, so changing it could point at a different mailbox. Jane.Smith@Old-Company.com becomes Jane.Smith@new-company.com.

The part the swap cannot check

A swap writes the address you expect, not an address that exists. If the new company changed its format, or two people shared one old address, the new address is wrong. When a server is asked to deliver to a mailbox that does not exist it normally answers with a 5.1.1 status (RFC 3463, bad destination mailbox address), and the message bounces for good. Only a mailbox check shows which swapped addresses are real.

Two old addresses can also become one. Run the result through remove duplicate emails. To find contacts whose company moved without telling you, use the company domain change checker.

What this cannot do

• It rewrites text and cannot tell whether the new mailbox exists.
• It assumes the part before the @ stayed the same.
• Two old addresses can become one. It counts these but does not remove them.
• Only the first sheet of a workbook is read.

Verify the new addresses

Upload the swapped list on the verify page: the first 100 email checks are free with a Google sign-in, no card. Each address comes back valid, risky or invalid with a reason, so you see which new addresses exist before you send. Nothing is sent to anyone on the list. For larger or recurring lists, see bulk email verification, list cleaning and pricing.

Swap your domains now

Upload the file to the email domain replacer.