ugh, sendgrid might not be a viable option. The incoming mail server at Bluehost blocked the test message sent through the sendgrid SMTP relay. Other IMAP servers will surely also block sendgrid SMTP relay.
I’ll try mailgun, but they require credit card data as a way of preventing abuse of their systems (no CC charge if usage is less than 10,000 mails/month).
550 "JunkMail rejected - o1678924164.outbound-mail.sendgrid.net [167.89.24.164]:44117 is in an RBL on rbl.unified-contact.com, see Blocked - see http://www.spamcop.net/w3m?action=checkblock&ip=167.89.24.164"
Update: I’m just going to use my home ISP for now. I have 587 option with them and very low volume of emails for the foreseeable future.