ORA-29279: SMTP permanent error: 501 Bad address syntax

While checking if procedure APEX_MAIL.SEND could send out a message to multiple users and being too lazy to open up the on-line help window and check what the documentation says, i made an attempt for sending a message to multiple recipients as follows:

begin
apex_mail.send(
p_to       => 'first@somedomain.com;second@somedomain.com',
p_from     => 'apex@someaddress.com',
p_body     => 'test message'
);
apex_mail.push_queue;
end;

But looking at view APEX_MAIL_QUEUE, i saw the message below in column MAIL_SEND_ERROR

ORA-29279: SMTP permanent error: 501 Bad address syntax

This is caused by the semicolon (;) used for separating the addresses.
Use commas (,) instead.

To delete undeliverable messages from APEX_MAIL_QUEUE, just execute:

delete from APEX_MAIL_QUEUE
where MAIL_SEND_ERROR is not null;

See message translations for ORA-29279 and search additional resources.

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ORA-29279: Errore permanente SMTP:
ORA-29279: error permanente de SMTP:
ORA-29279: error permanent de SMTP:
ORA-29279: erreur permanente SMTP :
ORA-29279: Permanenter SMTP-Fehler:
ORA-29279: μόνιμο σφάλμα SMTP:
ORA-29279: permanent SMTP-fejl:
ORA-29279: Permanent SMTP-fel:
ORA-29279: permanent SMTP-feil:
ORA-29279: pysyvä SMTP-virhe:
ORA-29279: SMTP állandó hiba:
ORA-29279: eroare permanentă SMTP:
ORA-29279: Permanente SMTP-fout:
ORA-29279: erro permanente de SMTP:
ORA-29279: erro permanente de SMTP:
ORA-29279: Постоянная ошибка SMTP:
ORA-29279: Permanentní chyba SMTP:
ORA-29279: trvalá chyba SMTP:
ORA-29279: trwały błąd SMTP:
ORA-29279: SMTP kalıcı hatası: