Why emails with attachments go to spam
Attachments are the most common way viruses and scams arrive by email, so filters look harder at any email that carries a file. A plain email from the same sender often sails through while the one with a file is held back.
Filters treat attachments as risky because malware spreads that way. Gmail and Outlook block program files such as .exe, .bat and .js, and Gmail can also block them inside .zip files and some password-protected archives. Gmail caps attachments at 25 MB per email, and Outlook.com at 25 MB per file. To stay out of spam, share a link (Google Drive, OneDrive) in first emails, use PDF, and keep files small.
Why attachments raise suspicion
- Malware rides on attachments. Fake invoices, shipping notices and "scanned documents" are the classic way ransomware gets in.
- Password-protected .zip files cannot be scanned, which is exactly why scammers use them.
- Office files with macros (.docm, .xlsm) can run code when opened.
- A stranger plus a file is the riskiest combination: a first-ever email with an attachment looks like phishing.
- Big files can bounce outright or be stripped.
- Scam patterns: "Your invoice is attached, open now", PDFs packed with links, and mismatched file names all add to the score.
Files Gmail and Outlook block
| Service | Blocked examples | Notes |
|---|---|---|
| Gmail | .exe, .bat, .cmd, .js, .jar, .msi, .vbs, .ps1, .scr, .lnk, .dll, .iso, .img, .dmg, .apk | Also blocked inside .zip and other archives, in some password-protected archives, and in documents with harmful macros |
| Outlook and Outlook.com | .exe, .bat, .js, .cmd, .vbs, .msi, .ps1, .scr, .lnk, .jar, .reg, .iso | .zip files are not blocked |
The full lists are longer; see the sources below. If you really need to send a blocked file type, share it through cloud storage instead.
Size limits
| Service | Attachment limit | What happens if bigger |
|---|---|---|
| Gmail | 25 MB in total | Gmail turns it into a Google Drive link |
| Outlook.com | 25 MB per file | Send up to 2 GB as a OneDrive link |
| Most business mail servers | Often 10 to 25 MB | The email bounces back |
Attachments grow by about a third when sent, so a 20 MB file can already be over the limit.
How to send files without landing in spam
- Share a link in first emails. Upload to Google Drive, OneDrive or Dropbox and send the link with clear sharing settings.
- Send attachments after they have replied once; a conversation builds trust.
- Prefer PDF over Word or Excel files with macros, and over .zip.
- Keep files small: compress photos and scans. See how to scan to email for small, clear PDFs.
- Name things clearly: "Invoice-1042-Sunny-Bakery.pdf" and a subject like "Invoice #1042 from Sunny Bakery".
- Set up your domain with SPF, DKIM and DMARC: check it with the free checker.
- Write a short, real message with the file. An email that is only an attachment looks automated.
Received a suspicious attachment?
Do not open it if you were not expecting it, even from someone you know: their account may have been hacked. Check with the sender another way, and use Report phishing in Gmail or Outlook if it is fake. See the Gmail spam folder and the Outlook junk folder.
Questions people ask
- Why do my emails with attachments go to spam but others do not?
- Attachments raise the risk score, especially in first emails to new people, large files, zip files and documents with macros. Send a link instead, or attach once the person has replied.
- Can I send a .zip file in Gmail?
- Usually yes. Gmail blocks a .zip that contains a blocked file type, and can block some password-protected archives.
- What is the maximum attachment size in Gmail?
- 25 MB in total. Larger files are sent as a Google Drive link automatically.
- Are PDF attachments safe?
- PDFs are the safest common format to send, but treat unexpected ones with care: scammers use them too.
Sending one email to a whole list? Check the addresses first with Veml, which removes bad and risky emails before you hit send. (Veml and EmailNa have the same owner.)