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Mail with Headers or Attachments
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When you send mail using the Mail API,
there are some restrictions on the headers that you can use and the types of
files you can attach.
An outgoing email has headers that provide details about the message, such as
the sender, recipient, date, and subject. Each header has a name and a value.
You can also include the following headers in an outgoing email; for security
purposes, other headers are not allowed:
- In-Reply-To
- List-Id
- List-Unsubscribe
- On-Behalf-Of
- References
- Resent-Date
- Resent-From
- Resent-To
Mail with attachments
An outgoing email message can have file attachments. Each attachment has a
filename and file data. The file data can come from any source, such as an
application data file or the datastore.
Filename extensions that are prohibited
As a security measure to protect against viruses, email attachments cannot use
the following filename extensions, and ZIP files cannot contain files with the
following filename extensions:
- ade
- adp
- bat
- chm
- cmd
- com
- cpl
- exe
- hta
- ins
- isp
- jse
- lib
- mde
- msc
- msp
- mst
- pif
- scr
- sct
- shb
- sys
- vb
- vbe
- vbs
- vxd
- wsc
- wsf
- wsh
Attachments and Multipurpose Internet Mail Extensions (MIME) types
The MIME type of an attachment is determined from the file's extension. The MIME
type identifies the type of content that is being sent, and can determine how
that data is transferred.
The following is a list of MIME types and their corresponding filename
extensions. You are not limited to these extensions, but if you use an unknown
extension, App Engine will assign it the MIME type application/octet-stream.
| MIME type |
Filename extensions |
| application/msword |
doc, docx |
| application/pdf |
pdf |
| application/rss+xml |
rss |
| application/vnd.google-earth.kml+xml |
kml |
| application/vnd.google-earth.kmz |
kmz |
| application/vnd.ms-excel |
xls, xlsx |
| application/vnd.ms-powerpoint |
pps, ppt, pptx |
| application/vnd.oasis.opendocument.presentation |
odp |
| application/vnd.oasis.opendocument.spreadsheet |
ods |
| application/vnd.oasis.opendocument.text |
odt |
| application/vnd.sun.xml.calc |
sxc |
| application/vnd.sun.xml.writer |
sxw |
| application/x-gzip |
gzip |
| application/zip |
zip |
| audio/basic |
au snd |
| audio/flac |
flac |
| audio/mid |
mid, rmi |
| audio/mp4 |
m4a |
| audio/mpeg |
mp3 |
| audio/ogg |
oga, ogg |
| audio/x-aiff |
aif, aifc, aiff |
| audio/x-wav |
wav |
| image/gif |
gif |
| image/jpeg |
jpeg, jpg, jpe |
| image/png |
png |
| image/tiff |
tiff, tif |
| image/vnd.wap.wbmp |
wbmp |
| image/x-ms-bmp |
bmp |
| text/calendar |
ics |
| text/comma-separated-values |
csv |
| text/css |
css |
| text/html |
htm, html |
| text/plain |
asc, c, diff, log, patch, pot, text, txt |
| text/x-vcard |
vcf |
| video/mp4 |
mp4 |
| video/mpeg |
mpeg, mpg, mpe |
| video/ogg |
ogv |
| video/quicktime |
qt, mov |
| video/x-msvideo |
avi |
Except as otherwise noted, the content of this page is licensed under the Creative Commons Attribution 4.0 License, and code samples are licensed under the Apache 2.0 License. For details, see the Google Developers Site Policies. Java is a registered trademark of Oracle and/or its affiliates.
Last updated 2025-08-29 UTC.
[[["Easy to understand","easyToUnderstand","thumb-up"],["Solved my problem","solvedMyProblem","thumb-up"],["Other","otherUp","thumb-up"]],[["Hard to understand","hardToUnderstand","thumb-down"],["Incorrect information or sample code","incorrectInformationOrSampleCode","thumb-down"],["Missing the information/samples I need","missingTheInformationSamplesINeed","thumb-down"],["Other","otherDown","thumb-down"]],["Last updated 2025-08-29 UTC."],[[["\u003cp\u003eWhen using the Mail API, there are specific limitations on the headers you can include, with only a defined list of headers being permitted for security reasons.\u003c/p\u003e\n"],["\u003cp\u003eOutgoing emails can include file attachments, with the file data potentially coming from various sources within your application.\u003c/p\u003e\n"],["\u003cp\u003eCertain file extensions are prohibited for email attachments and within ZIP files due to security risks, including extensions like \u003ccode\u003e.exe\u003c/code\u003e, \u003ccode\u003e.bat\u003c/code\u003e, and \u003ccode\u003e.vbs\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eThe MIME type of an email attachment is determined by its file extension, and while many common extensions are recognized, unknown extensions are defaulted to \u003ccode\u003eapplication/octet-stream\u003c/code\u003e.\u003c/p\u003e\n"],["\u003cp\u003eThe provided content lists the supported MIME types and their corresponding file extensions, giving a clear guide to users.\u003c/p\u003e\n"]]],[],null,["# Mail with Headers or Attachments\n\nWhen you send mail using the [Mail API](/appengine/docs/legacy/standard/php/mail),\nthere are some restrictions on the headers that you can use and the types of\nfiles you can attach.\n| This API is supported for first-generation runtimes and can be used when [upgrading to corresponding second-generation runtimes](/appengine/docs/standard/\n| php-gen2\n|\n| /services/access). If you are updating to the App Engine PHP 7/8 runtime, refer to the [migration guide](/appengine/migration-center/standard/migrate-to-second-gen/php-differences) to learn about your migration options for legacy bundled services.\n\nOptional headers you can use\n----------------------------\n\nAn outgoing email has headers that provide details about the message, such as\nthe sender, recipient, date, and subject. Each header has a name and a value.\nYou can also include the following headers in an outgoing email; for security\npurposes, other headers are not allowed:\n\n- In-Reply-To\n- List-Id\n- List-Unsubscribe\n- On-Behalf-Of\n- References\n- Resent-Date\n- Resent-From\n- Resent-To\n\nMail with attachments\n---------------------\n\nAn outgoing email message can have file attachments. Each attachment has a\nfilename and file data. The file data can come from any source, such as an\napplication data file or the datastore.\n\n### Filename extensions that are prohibited\n\nAs a security measure to protect against viruses, email attachments cannot use\nthe following filename extensions, and ZIP files cannot contain files with the\nfollowing filename extensions:\n\n- ade\n- adp\n- bat\n- chm\n- cmd\n- com\n- cpl\n- exe\n- hta\n- ins\n- isp\n- jse\n- lib\n- mde\n- msc\n- msp\n- mst\n- pif\n- scr\n- sct\n- shb\n- sys\n- vb\n- vbe\n- vbs\n- vxd\n- wsc\n- wsf\n- wsh\n\n### Attachments and Multipurpose Internet Mail Extensions (MIME) types\n\nThe MIME type of an attachment is determined from the file's extension. The MIME\ntype identifies the type of content that is being sent, and can determine how\nthat data is transferred.\n\nThe following is a list of MIME types and their corresponding filename\nextensions. You are not limited to these extensions, but if you use an unknown\nextension, App Engine will assign it the MIME type `application/octet-stream`."]]
