Summary Message Commands
S y
Yank the current article into an already existing Message composition buffer (gnus-summary-yank-message). This command prompts for what message buffer you want to yank into, and understands the process/prefix convention (see Process/Prefix).
S A
Attach the current article into an already existing Message composition buffer (gnus-summary-attach-message). If no such buffer exists, a new one is created. This command prompts for what message buffer you want to yank into, and understands the process/prefix convention (see Process/Prefix).