PHPMailer SMTP错误：无法连接到SMTP主机

PHPMailer有一个奇怪的问题，它显示一个SMTP连接错误，如下所示 . 什么可能导致这个？它在我使用Gmail SMTP服务器时有效，并且还可以使用本地邮件功能 . 服务器上的Roundcube发送正常 . 它似乎只是PHPMailer . 据我所知，所有设置都是正确的 . 它正在使用TLS，我尝试了不同的端口 . 正确的端口显示以下错误：

2016-05-05 21:58:47 Connection: opening to mail.myserver.com:587, timeout=300, options=array (
                                      )
2016-05-05 21:58:47 Connection: opened
2016-05-05 21:58:52 SMTP -> get_lines(): $data is ""
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "220 sys.myserver.com ESMTP Exim 4.72 Thu, 05 May 2016 17:58:50 -0400
                                      "
2016-05-05 21:58:52 SERVER -> CLIENT: 220 sys.myserver.com ESMTP Exim 4.72 Thu, 05 May 2016 17:58:50 -0400
2016-05-05 21:58:52 CLIENT -> SERVER: EHLO localhost
2016-05-05 21:58:52 SMTP -> get_lines(): $data is ""
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "250-sys.myserver.com Hello ***********]
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $data is "250-sys.myserver.com Hello cpc68331-cdif16-2-0-cust906.5-1.cable.virginm.net [86.3.207.139]
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "250-SIZE 52428800
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $data is "250-sys.myserver.com Hello cpc68331-cdif16-2-0-cust906.5-1.cable.virginm.net [86.3.207.139]
                                      250-SIZE 52428800
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "250-PIPELINING
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $data is "250-sys.myserver.com Hello ***************************]
                                      250-SIZE 52428800
                                      250-PIPELINING
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "250-AUTH PLAIN LOGIN
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $data is "250-sys.myserver.com Hello ****************************]
                                      250-SIZE 52428800
                                      250-PIPELINING
                                      250-AUTH PLAIN LOGIN
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "250-STARTTLS
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $data is "250-sys.myserver.com Hello ******************]
                                      250-SIZE 52428800
                                      250-PIPELINING
                                      250-AUTH PLAIN LOGIN
                                      250-STARTTLS
                                      "
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "250 HELP
                                      "
2016-05-05 21:58:52 SERVER -> CLIENT: 250-sys.myserver.com Hello ***************]
                                      250-SIZE 52428800
                                      250-PIPELINING
                                      250-AUTH PLAIN LOGIN
                                      250-STARTTLS
                                      250 HELP
2016-05-05 21:58:52 CLIENT -> SERVER: STARTTLS
2016-05-05 21:58:52 SMTP -> get_lines(): $data is ""
2016-05-05 21:58:52 SMTP -> get_lines(): $str is  "220 TLS go ahead
                                      "
2016-05-05 21:58:52 SERVER -> CLIENT: 220 TLS go ahead
2016-05-05 21:58:52 SMTP Error: Could not connect to SMTP host.
2016-05-05 21:58:52 CLIENT -> SERVER: QUIT
2016-05-05 21:58:53 SMTP -> get_lines(): $data is ""
2016-05-05 21:58:53 SMTP -> get_lines(): $str is  "����221 sys.myserver.com closing connection
                                      "
2016-05-05 21:58:53 SMTP -> get_lines(): $data is "����221 sys.myserver.com closing connection
                                      "
2016-05-05 21:58:53 SMTP -> get_lines(): $str is  ""
2016-05-05 21:58:53 SERVER -> CLIENT: ����221 sys.myserver.com closing connection
2016-05-05 21:58:53 SMTP ERROR: QUIT command failed: ����221 sys.myserver.com closing connection


----------


2016-05-05 21:58:53 Connection: closed
2016-05-05 21:58:53 SMTP connect() failed. https://github.com/PHPMailer/PHPMailer/wiki/Troubleshooting
{"success":1,"id":"3391"}