Here are the commands to create a summary for the current Rmail buffer. Once the Rmail buffer has a summary, changes in the Rmail buffer (such as deleting or expunging messages, and getting new mail) automatically update the summary.

h, C-M-h

Summarize all messages (rmail-summary).

l labels RET, C-M-l labels RET

Summarize messages that have one or more of the specified labels (rmail-summary-by-labels).

C-M-r rcpts RET

Summarize messages that match the specified recipients (rmail-summary-by-recipients).

C-M-t topic RET

Summarize messages that have a match for the specified regexp topic in their subjects (rmail-summary-by-topic).

C-M-s regexp RET

Summarize messages whose headers match the specified regular expression regexp (rmail-summary-by-regexp).

C-M-f senders RET

Summarize messages that match the specified senders. (rmail-summary-by-senders).

The h or C-M-h (rmail-summary) command fills the summary buffer for the current Rmail buffer with a summary of all the messages in the buffer. It then displays and selects the summary buffer in another window. C-M-l /labels/ =RET= (rmail-summary-by-labels) makes a partial summary mentioning only the messages that have one or more of the labels labels. labels should contain label names separated by commas. C-M-r /rcpts/ =RET= (rmail-summary-by-recipients) makes a partial summary mentioning only the messages that have one or more recipients matching the regular expression rcpts. This is matched against the To, From, and CC headers (supply a prefix argument to exclude the CC header). C-M-t /topic/ =RET= (rmail-summary-by-topic) makes a partial summary mentioning only the messages whose subjects have a match for the regular expression topic. With a prefix argument, the match is against the whole message, not just the subject. C-M-s /regexp/ =RET= (rmail-summary-by-regexp) makes a partial summary that mentions only the messages whose headers (including the date and the subject lines) match the regular expression regexp. C-M-f /senders/ =RET= (rmail-summary-by-senders) makes a partial summary that mentions only the messages whose From fields match the regular expression senders. Note that there is only one summary buffer for any Rmail buffer; making any kind of summary discards any previous summary. The variable rmail-summary-window-size says how many lines to use for the summary window. The variable rmail-summary-line-count-flag controls whether the summary line for a message should include the line count of the message. Setting this option to nil might speed up the generation of summaries.