Unable to send mail: 5.3.3 Unrecognized command

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Hello,

I recently updated to 6.2.1 and have since been unable to send mail via SMTP. I've checked with the guy that runs the mail server and he tells me there have been no changes at his end. I am getting the following error in the log:

Mail Exception Occurred. Unable to send mail: 5.3.3 Unrecognized command
#0 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/libraries/3rdparty/Zend/Mail/Protocol/Smtp.php(205): Zend_Mail_Protocol_Abstract->_expect(220, 180)
#1 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/libraries/3rdparty/Zend/Mail/Transport/Smtp.php(200): Zend_Mail_Protocol_Smtp->helo('localhost')
#2 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/libraries/3rdparty/Zend/Mail/Transport/Abstract.php(348): Zend_Mail_Transport_Smtp->_sendMail()
#3 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/libraries/3rdparty/Zend/Mail.php(1194): Zend_Mail_Transport_Abstract->send(Object(Zend_Mail))
#4 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/core/helpers/mail.php(349): Zend_Mail->send(Object(Zend_Mail_Transport_Smtp))
#5 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/core/controllers/blocks/form.php(454): Concrete5_Helper_Mail->sendMail()
#6 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/core/models/block.php(411): Concrete5_Controller_Block_Form->action_submit_form()
#7 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/startup/process.php(283): Concrete5_Model_Block->passThruBlock('submit_form')
#8 /home/[USER]/public_html/updates/concrete5.6.1.2_updater/concrete/dispatcher.php(244): require('/home/[USER]/p...')
#9 /home/[USER]/public_html/concrete/startup/updated_core_check.php(6): require('/home/[USER]/p...')
#10 /home/[USER]/public_html/concrete/dispatcher.php(20): require('/home/[USER]/p...')
#11 /home/[USER]/public_html/index.php(2): require('/home/[USER]/p...')
#12 {main}
Template Used: block_form_submission


Any help would be very much appreciated!

Thanks in advance! Ross.

Environment:
# concrete5 Version
5.6.1.2
# concrete5 Packages
Clevyr Tweets (1.0), Designer Content (2.1.2), Email List Signup (1.03), Facebook Like Button (1.1), Fancy Image Links (1.3.5), Flowplayer Free (1.1.0), Galleria image gallery (2.0), Gallerific (1.1.2), Image Caption (1.5.1), Mailing List (2.36), MindNet Optimize MySQL database (1.11), Page List Title (2.3), PHP block by ND (1.0), ProEvents (9.0.3), Random Image (1.0.1), Sortable Fancybox Gallery (1.17).
# concrete5 Overrides
blocks/next_previous, blocks/slider, blocks/jb_gallerific, blocks/homepage_slider, blocks/search, blocks/email_list_signup, blocks/thumbslider, blocks/autonav, blocks/pro_event_list, blocks/content, blocks/page_list, blocks/tony_mailing_list, blocks/guestbook, blocks/page_list_title, single_pages/page_not_found.php, single_pages/login.php, themes/404, themes/RMD
# Server Software
Apache/2.2.22 (Unix) mod_ssl/2.2.22 OpenSSL/0.9.8e-fips-rhel5 DAV/2 mod_auth_passthrough/2.1 mod_bwlimited/1.4 FrontPage/5.0.2.2635
# Server API
cgi-fcgi
# PHP Version
5.3.10
# PHP Extensions
bcmath, calendar, cgi-fcgi, Core, ctype, curl, date, dom, ereg, exif, filter, ftp, gd, gettext, hash, iconv, imap, ionCube Loader, json, libxml, mbstring, mcrypt, mysql, mysqli, openssl, pcre, PDO, pdo_mysql, pdo_sqlite, Phar, posix, pspell, Reflection, session, SimpleXML, soap, sockets, SourceGuardian, SPL, SQLite, sqlite3, standard, tidy, timezonedb, tokenizer, wddx, xml, xmlreader, xmlrpc, xmlwriter, xsl, Zend Guard Loader, zip, zlib.
# PHP Settings

RMDWebDesign
 
Remo replied on at Permalink Reply
Remo
I think you've specified to use a TLS encryption but the mail server doesn't support this.

Can you please post the SMTP Method settings you've entered in concrete5?
RMDWebDesign replied on at Permalink Reply 1 Attachment
RMDWebDesign
Thanks for your reply Remo!

You are right, I am using TLS, but at the mail server admins request.