go-simple-mail v2.2.1 Release NotesRelease Date: 2019-10-16 // almost 2 years ago
smtp.go: expectCode correction for RCPT for match 25x return code.
Earlier versions match only 250.
Match 25x return like valid code the 251 (User not local; will forward to )
🗄 251 code is deprecated in SMTP, but who knows who still uses it.