Xerox doesn't mark it as spam, it can't. Your issue would be with Gmail.
The aspmx server is also only capable of sending m,ail to other gmail hosted email addresses, I would switch to smtp.gmail.com, port 587 and use STARTTLS encryption.
For the spam thing, change the email subject line/ message body and attachment name.
This is all run of the mill stuff that should be done anyway, but using the aspmx server means you will need to do this fairly often, since the server doesn't require authentication, it is extra stringent so as to deter spammers from using it, where smtp.gmail.com is authenticated that isn't the case.
Latest firmware for your devices is highly preferred to keep in line with new SHA-2 requirement's for TLS support.
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