Forward a message as is, including leaving the original headers intact, only appending the Resent-* headers. The message should appear to the final recipient as if it was sent directly by the original sender (except for the Resent-* headers and headers appended by the final recipient's server). For implementation details, please refer to neomutt's bounce-message command.

...and operate on them at once, in particular select multiple attachments and save them under the same directory within a single :save command invocation.

aerc could support additional placeholders to be used with the index-format setting, for instance attachment status (does the email contain any attachments?) and message size.

Something like ranger's task window, where for instance statuses of yet unsent (due to poor network for example) outgoing messages would be displayed, perhaps with the possibility to cancel or edit them, could be nice. #84 could also profit from this. Other background tasks could be displayed there as well.

Just some of my thoughts: it seems reasonable to me that the cache should be used for client-side threading, at least for the messages that have already been fetched. For instance, neomutt downloads the headers for the full folder upon its opening, which of course causes a significant delay (just the first time with header cache enabled, though), perhaps aerc could do the same in the background? Preferably with a setting saying how many messages should be cached, e. g.: viewed (the current behaviour)/n (n newest messages)/since (messages new than a given date)/all.

For instance, typing :save -f /tm<Tab><Tab> on a message or an attachment completes :save /tmp instead of the expected :save -f /tmp.

Tested with aerc 0.13.0.