smtp: verify the certificate of the SMTP server for STARTTLS/SMTPS Before this patch, the certificate of the SMTP server for STARTTLS or SMTPS isn't verified. This may cause man-in-the-middle security problem (stealing authentication information), even though SMTP channel itself is encrypted by SSL. When "[smtp] tls" is configured as "smtps" or "starttls", this patch: - uses classes introduced by preceding patches instead of "SMTP" or "SMTP_SSL" of smtplib, and - verifies the certificate of the SMTP server, if "[smtp] verifycert" is configured as other than False "[smtp] verifycert" can be configured in 3 levels: - "strict": This verifies peer certificate, and aborts if: - peer certification is not valid, or - no configuration in "[hostfingerprints]" and "[web] cacerts" This is default value of "[smtp] verifycert" for security. - "loose": This verifies peer certificate, and aborts if peer certification is not valid. This just shows warning message ("certificate not verified"), if there is no configuration in "[hostfingerprints]" and "[web] cacerts". This is as same as verification for HTTPS connection. - False(no verification): Peer certificate is not verified. This is as same as the behavior before this patch series. "hg email --insecure" uses "loose" level, and ignores "[web] cacerts" as same as push/pull/etc... with --insecure. Ignoring "[web] cacerts" configuration for "hg email --insecure" is already done in "dispatch._dispatch()" by looking "insecure" up in the table of command options.