According to http://www.greenend.org.uk/rjk/tech/smtpreplies.html http://www.greenend.org.uk/rjk/tech/smtpreplies.html, SMTP server can give you either a tempor

According to http://www.greenend.org.uk/rjk/tech/smtpreplies.html http://www.greenend.org.uk/rjk/tech/smtpreplies.html, SMTP server can give you either a temporary error (452 - Requested action not taken: insufficient system storage) or permanent error (552 - Requested mail action aborted: exceeded storage allocation). Maybe there are some heuristics that are used for this...?