That's probably a question for Gmail.
But if you are asking:
-
if I either SMTP or use the API is the inbound transmission secure?
-- Gmail insists on a SSL/TLS connection from SMTP. So it should be difficult to snif the data in transit. The API uses SSL (like a padlock website would)
-
once in Gmail server do I need to worry about security?
-- difficult to definitely answer. But probably fine for most things. If you were an Enemy of the state you might worry what can be accessed with special power...
- if the end recipient uses a 'less secure' client couldthe email.becoke insecure.
-- two issues here. Can the client use IMAP/POP to read the email with no encryption AND does it let you save attachments etc to the (?insecure) desktop?
--- IMAP and POP security is enabled, so that bit should be fine. But... The client is always the challenge. But you are now waay beyond anything that R should need to factor in.