Splitting emails by domain is the foundation before live/die checks. Mixed lists forced through one tool muddy Invalid/Unknown rates and hide which provider caused errors. This guide splits Gmail, Yahoo, Outlook, AOL, GMX, and Mail.com into separate files and routes each to a matching checker.
Why split by domain?
- Most checkers expect a domain family — mixed files add noise.
- Available/Taken reports by provider only make sense on split inputs.
- Rechecking Unknown per group is cheaper and clearer.
Prep: extract emails before you filter
If the source still mixes notes, URLs, phones, or multi-column text, pull a pure email list first. Text Data Extractor helps when data is not yet one-email-per-line.
- Back up the original file.
- Extract emails → save
emails_all.txt. - Dedupe and drop blank lines.
- Only then start domain filters.
Split rule: use the part after @
For each local@domain line, use lowercase domain as the bucket key. Common groups:
| File group | Common domains | Suggested checker |
|---|---|---|
| gmail | gmail.com, googlemail.com | Gmail Username Checker |
| yahoo | yahoo.com (and Yahoo variants you keep) | Yahoo Checker |
| outlook | hotmail.com, outlook.com, live.com | Hotmail/Outlook Checker |
| aol | aol.com | AOL Checker |
| gmx | gmx.com, gmx.de, gmx.net… | GMX Checker |
| mailcom | mail.com and Mail.com-family domains in your list | Mail.com Checker |
| other | everything else | handle later / other tools |
Name files clearly: split_gmail.txt, split_yahoo.txt… and keep emails_all.txt as the source of truth.
Suggested split workflow
- Lowercase domains so
Gmail.comdoes not land in the wrong bucket. - Filter each group against your domain allow-list.
- Count rows per file — catch skewed lists early.
- Scan for invalid formats (missing @, spaces) before checker import.
- Only run checks after each group file is clean.
After splitting: route to checkers
You do not need all six tools if a domain is absent. Prioritize high-volume groups. For each group:
- Pilot 50–200 rows.
- Export Available/Taken/Invalid/Unknown separately.
- Recheck Unknown inside that same group.
Common split mistakes
- Filtering before extraction — emails mid-sentence get missed.
- Splitting hotmail/outlook/live too finely — or forgetting to group them when one Microsoft checker covers all three.
- Deleting “other” too early — data you need later disappears.
- Overwriting the original while testing filter rules.
Related tools on ToolMMO
- Text Data Extractor
- Gmail Username Checker
- Hotmail/Outlook Checker
- Yahoo Checker
- AOL Checker
- GMX Checker
- Mail.com Checker
Conclusion
Domain splits are a cheap habit with a large effect on check quality. Extract → normalize → filter after @ → keep an other file → then run checkers. Start with the highest-volume group and preserve the source file for audits.