I am getting and error when sending emails with resend relay.
the log is
urbackup | < 450 The `to` field must be a `string`.
urbackup | * Connection #0 to host smtp.resend.com left intact
urbackup | 2024-09-25 14:46:56: WARNING: Error sending mail to "receiver@example2.com". Failure when receiving data from the peer(ec=56), . Retrying in 30m
urbackup | * Trying 66.51.120.219:465...
urbackup | * Connected to smtp.resend.com (66.51.120.219) port 465 (#0)
urbackup | * WARNING: failed to load NSS PEM library libnsspem.so. Using OpenSSL PEM certificates will not work.
urbackup | * CAfile: none
urbackup | * CApath: none
urbackup | * skipping SSL peer certificate verification
urbackup | * SSL connection using TLS_AES_256_GCM_SHA384
urbackup | * Server certificate:
urbackup | * subject: CN=*.resend.com
urbackup | * start date: Aug 27 13:30:51 2024 GMT
urbackup | * expire date: Nov 25 13:30:50 2024 GMT
urbackup | * common name: *.resend.com
urbackup | * issuer: CN=E5,O=Let's Encrypt,C=US
urbackup | < 220 Resend SMTP Relay ESMTP
urbackup | > EHLO 57b38d998787
urbackup | < 250-Resend SMTP Relay Nice to meet you, [172.16.132.58]
urbackup | < 250-PIPELINING
urbackup | < 250-8BITMIME
urbackup | < 250-SMTPUTF8
urbackup | < 250-AUTH PLAIN LOGIN
urbackup | < 250 SIZE 10485760
urbackup | > AUTH PLAIN
urbackup | < 334
urbackup | > redactedkey
urbackup | < 235 Authentication successful
urbackup | > MAIL FROM:<sender@example.com>
urbackup | < 250 Accepted
urbackup | > RCPT TO:<receiver@example2.com>
urbackup | < 250 Accepted
urbackup | > DATA
urbackup | < 354 End data with <CR><LF>.<CR><LF>
urbackup | < 450 The `to` field must be a `string`.
urbackup | * Connection #0 to host smtp.resend.com left intact
urbackup | 2024-09-25 14:46:58: WARNING: Error sending mail to "receiver@example2.com". Failure when receiving data from the peer(ec=56), . Retrying in 30m
This works fine if sent to the same email when I used a different smtp server
450 The `to` field must be a `string`.
seems to be the problem.
What’s even more interesting is that the to field when sent with a different smtp server is blank in the email client.