I reply to an email from a gmail address asking for an attachment. It gets it flagged as a "security issue".
Fine...rewrite email, stuff file into a tgz archive since that's apparently ok.
gmail: nope.
OK, I upload the file to a server, include link in email replying to original request for a file.
gmail: no.
Fine, email person who emailed me and tell them about the issue, to arrange another method.
gmail: we're flagging your repeated attempts to send email as suspicious.