Double-check the address properties are absolutely identical to what they use (like a dot in name, etc)
Make sure you put something proper in Subject line .. Nothing is bad, as are "spammy words" Use a string of words that dont look like spam. These can be wiped from server.
Don't use web addresses in subject line ... Can get wiped at ISP.
Photos attached? If possible, zip them up and attach.
If you have a rude/odd/naughty email name .. make sure your friends add it to their server (ISP) webmail setup as an "ok to deliver/not spam" address.