[grincho]

Things (https://culturedcode.com/things/) does pretty much that. It has a little Quick Entry daemon which lets you press control-option-space in Mail.app to make a new task linked to the selected mail. By default, the subject ends up as the task's title, though you can change it before hitting Return.

In general, I highlight recommend Things. It does all the typical GTD stuff, in a mostly Maclike way, and has a great iOS client.

[Edit: In fact, you can actually drag a mail right into a Things window as well, just as you propose. I never knew that!]

[yodon]

Can you click on a created task in Things and get back to the mail message in the iOS Mail app (as opposed to just seeing a copy of the message as text in the todo app the way most todo apps handle email->task connections)?

[grincho]

Absolutely. The links even resolve on different devices, as long as you have access to the same mail accounts.

[yodon]

Looks like I just blew $10 on this.

The iPad version allows you to create tasks truly linked to emails but the iPhone version doesnt let you create them you can only open them (from what I can find, hopefully I’m wrong as I’ve been looking for this feature for YEARS and would love to make this app home)