smptplib problem SMTPRecipientsRefused for emails with ! exclamation mark in local portion of email

[Radomir Wojcik]

No need to do more troubleshooting, need to update the config. Found that exim default config denies these so nothing to do with smptlib indeed:

What this statement is doing is to accept unconditionally all recipients in messages that are submitted by SMTP from local processes using the standard input and output (that is, not using TCP/IP). A number of MUAs operate in this manner.

deny    message       = Restricted characters in address
        domains       = +local_domains
        local_parts   = ^[.] : ^.*[@%!/|]

deny    message       = Restricted characters in address
        domains       = !+local_domains
        local_parts   = ^[./|] : ^.*[@%!] : ^.*/\\.\\./
These statements are concerned with local parts that contain any of the characters "@", "%", "!", "/", "|", or dots in unusual places. Although these characters are entirely legal in local parts (in the case of "@" and leading dots, only if correctly quoted), they do not commonly occur in Internet mail addresses.

http://www.exim.org/exim-html-current/doc/html/spec_html/ch-the_default_configuration_file.html