I agree it's a useful facility, but Mail doesn't offer it as such. You could look at this (quoted from the Help):
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If you're traveling, or are in a hurry, you might want to leave large messages on your Post Office Protocol (POP) mail server so you can retrieve them later when you have more time or a faster connection.
Choose Mail > Preferences and click Accounts.
Select a POP account.
Click Advanced, then enter the maximum size of messages you want to retrieve automatically next to “Prompt me to skip messages over.” (For example, 100 KB.)
When you receive a message that is larger than the size you specified, Mail gives you the option of downloading the message, skipping it and leaving it on the server, or deleting it from the server. If you don't make a choice within 15 seconds, Mail automatically downloads the message. If you skip a message, then the next time you open Mail you're asked again to download, skip, or delete the message.
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Not sure whether you get the header when this happens, you would have to experiment.
_________________________________________________
If you're traveling, or are in a hurry, you might want to leave large messages on your Post Office Protocol (POP) mail server so you can retrieve them later when you have more time or a faster connection.
Choose Mail > Preferences and click Accounts.
Select a POP account.
Click Advanced, then enter the maximum size of messages you want to retrieve automatically next to “Prompt me to skip messages over.” (For example, 100 KB.)
When you receive a message that is larger than the size you specified, Mail gives you the option of downloading the message, skipping it and leaving it on the server, or deleting it from the server. If you don't make a choice within 15 seconds, Mail automatically downloads the message. If you skip a message, then the next time you open Mail you're asked again to download, skip, or delete the message.
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Not sure whether you get the header when this happens, you would have to experiment.
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Free Header Downloads
![Download Headers Only In Mac Mail Download Headers Only In Mac Mail](https://www.officetooltips.com/images/tips/131_2003/3.png)
Outlook Only Download Headers
For normal users, I'd imagine this is fine. We have some institutional users with 20+ years of email (hundreds of thousands of messages), and this new feature of Mac Mail is slowing their computers down significantly. My manager said that Mail.app previously just downloaded message headers, but now it's downloading full text and attachments. Download Headers and then Full Items – first Outlook grabs all the message headers, then it downloads the rest of the content in each message. Depending on the speed of the connection, this gives you a chance to delete any messages (as headers) before the entire message is downloaded. Download Headers – only the message headers are.