sending email with PHP Swiftmailer and put into the SentBox using imap protocol.

put_sent_mail_into_the_mailbox_using_imap.php

<?php
$message = (new Swift_Message('Wonderful Subject'))
    ->setFrom(['noreply@example.org' => 'John Doe'])
    ->setReplyTo('reply@example.org', 'Reply To')
    ->setTo(['receiver@domain.org', 'other@domain.org' => 'A name'])
    ->setBody('mail body', 'text/html')
;

// Swiftmail 는 sent box 에 남기지 않으므로 아래 꽁수로 imap_처리
// https://stackoverflow.com/questions/19497557/add-mail-to-send-folder-with-swiftmailer
$stream = null;

$try_count = 0;
retry:
try {
    $stream = \imap_open("{imap.naver.com/imap/ssl/novalidate-cert}",
        'user',
        'password',
        null,
        1,
        ['DISABLE_AUTHENTICATOR' => 'GSSAPI']);

} catch (\Exception $exception){
    /**
     * 가끔 아래와 같은 예외와 함게 imap_open 에러가 발생함. 이런 경우 sleep 후에 재시도
     *
     * Whoops\Exception\ErrorException  : Unknown: [AUTH] Sorry, IMAP UserAuth Server Is Checking..Please, Try later. (errflg=1)
     *
     */
    $this->info("imap exception. retrying... $try_count ");
    sleep(3);

    if ($try_count++ < 3) {
        goto retry;
    }
}

$msg = $message->toString();
// connect to IMAP SSL (port 993) without Kerberos and no certificate validation
\imap_append($stream, "{imap.naver.com/imap/ssl/novalidate-cert}Sent Items", $msg . "\r\n", "\\Seen");

// Saves message to Sent folder and marks it as read

\imap_close($stream);