IMAP backend compatibility with Windows 10 WindowsMail

[ray-magini]

Hi, First to say: Really great work! :)

While sending an email with WindowsMail on Windows 10 via the IMAP backend the "From" header delivered by the MUA appears to be empty and therefore the send fails.

28/03/2016 20:21:13 [ 4558] [WBXML] [dirk] [XXXXXXXXXXXXXXXX] I MIME-Version: 1.0 To: Dirk Dietrich dirk@homedietrich.de From: Subject: XYZ Date: Mon, 28 Mar 2016 20:21:13 +0200 Importance: normal

For me the below fix in backend/imap/imap.php (around line 2552) on the from header-check helped that it falls back to the default "from" address.

I tried to commit it via pull request but it did not work because of permission rights so maybe someone can assist go review it and get it in.

    if (isset($headers["from"]) **&& strlen($headers["from"]) > 0**) {
        ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFromHeaderValue(): from defined: %s", $headers["from"]));
        if (strlen(IMAP_DEFAULTFROM) > 0) {
            ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFromHeaderValue(): Overwriting From: %s", $from));
            $headers["from"] = $from;
        }
    }
    elseif (isset($headers["From"]) **&& strlen($headers["From"]) > 0**) {
        ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFromHeaderValue(): From defined: %s", $headers["From"]));
        if (strlen(IMAP_DEFAULTFROM) > 0) {
            ZLog::Write(LOGLEVEL_DEBUG, sprintf("BackendIMAP->getFromHeaderValue(): Overwriting From: %s", $from));

Cheers, Dirk