Describe the bug
sender/sender.go:188:
headers["References"] = strings.Join(references, " ") + " " + inReplyTo
A long thread (deep replies, list traffic) easily produces a References line over RFC 5322's 998-octet limit. Some MTAs reject the message; others silently truncate.
Expected behavior
Fold the header at 78 chars (RFC 5322 §2.2.3) and trim oldest IDs from the middle if over the limit.
Describe the bug
sender/sender.go:188:A long thread (deep replies, list traffic) easily produces a References line over RFC 5322's 998-octet limit. Some MTAs reject the message; others silently truncate.
Expected behavior
Fold the header at 78 chars (RFC 5322 §2.2.3) and trim oldest IDs from the middle if over the limit.