Reply via client breaks when message too large

When the message being replied too is too large (working theory; could possibly be odd characters but doesn't seem so), the Reply via your own mail client silently fails.

Sample message that fails:
https://lists.apache.org/thread.html/f2ba557c69611535038bdb24451ab725ae950aaf917983c18a996b27@%3Cdev.ponymail.apache.org%3E

Mac/Chrome/Version 53.0.2785.143 (64-bit) with Thunderbird as default mail client (which works for short messages).

Chrome developer tools shows the GET mailto:... link was clicked, but (cancelled). It seems to have the right headers and start of the email body content.

It's likely various client OS/browsers/mail clients have slightly different max URL lengths. Possible enhancements are either clipping the mailto: at some default max length, or somehow otherwise abbreviating or shortening some reply-level in the body somehow (but that would be arbitrary).

Start by tracing the Reply via your own mail client mailto: link described in the issue and reproduce it with the sample message in Chrome and Thunderbird. Determine how oversized reply content is handled, then verify that the chosen handling prevents silent failure while preserving replies for shorter messages.

Written by the indexing model from the issue text.