In macOS mail, you are forced to attach files inline in the message. I am aware you can enable "Always Insert Attachments at End of Message" in the menubar's Edit menu, but I understand this still leaves the attachment inline. Even when an image or PDF is shown as an icon at the end of the message in macOS Mail, the recipient ends up seeing the attachment as a huge inline image.

Is there an actual difference in "inline" vs. "non-inline" attachments in email protocol? Or do other apps technically attach things inline at the end, just visually showing it differently?

1 Answer 1


There is a definition in the MIME specification for both inline and attachment files within email messages, but (from the Wiki page linked above):

As of 2010, a good majority of mail user agents do not follow this prescription fully. Most users are unaware of how to set the content-disposition to attachment. Many mail user agents also send messages with the file name in the name parameter of the content-type header instead of the filename parameter of the content-disposition header. This practice is discouraged.

In short, whether the sender and recipient follow the spec, or do things differently, is uncertain.

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    This is exactly what I was hoping to understand, thank you. Am I correct in my understanding that macOS Mail doesn't allow attachment-type attachments, then? That's what I'm really wondering. To take it a step further, how do the most commonly used email clients deal with attachments? I imagine Gmail's web interface is one of those, and perhaps Airmail, Spark, Outlook, etc.?
    – gills
    May 22, 2019 at 19:38
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    For the record, I've just read several discussions of this issue on various forums, and none of them are very clear. Additionally, many are out of date. benwiggy's answer was very helpful. If anyone could answer etudes' good follow-up questions, that would be great. Apr 3, 2020 at 15:05

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