You might have some luck grabbing their DNS records, look for TXT records with the string "spf" in them. If they're a big sender of email, they've likely needed

You might have some luck grabbing their DNS records, look for TXT records with the string "spf" in them. If they're a big sender of email, they've likely needed to add SPF records (referencing their transactional email service of choice) to their DNS, in order for their emails to avoid the spambox.