Hello. Sometimes google rejects messages for dkim errors. The below is an error message from a blocked message I sent to someone with whom I had been successfully corresponding. Repeated attempts generate the same error. How can I resolve this? I see similar issues me tioned in your community forum.

Error Type: SMTP
Remote server (142.250.102.26) issued an error.
hMailServer sent: .
Remote server replied: 550-5.7.26 This mail is unauthenticated, which poses a security risk to the
550-5.7.26 sender and Gmail users, and has been blocked. The sender must
550-5.7.26 authenticate with at least one of SPF or DKIM. For this message,
550-5.7.26 DKIM checks did not pass and SPF check for [kannoncom.com] did not
550-5.7.26 pass with ip: [162.216.242.37]. The sender should visit
550-5.7.26 https://support.google.com/mail/answer/81126#authentication for
550 5.7.26 instructions on setting up authentication. o5-20020a170906774500b008c580ab8d9esi8642798ejn.69 - gsmtp

Gregg Kaloust

https://www.dynu.com/en-US/Blog/Article?Article=Google-rejecting-emails-due-to-spf-and-DKIM-failures