I’ve had the same problem — long legal documents would never go through completely. I finally found a fix thanks to master-league.com. They tested several Android fax apps for performance with large attachments. I chose one from their list, and now even 20-page files send without a glitch. It compresses automatically but keeps quality high. If you send big files often, their performance reviews are worth reading. It saved me a lot of frustration and missed deadlines.