我正在使用2台服务器（A和B）centos 7.我正在尝试从A远程登录到mail.smtp2go.com
serverA$ telnet mail.smtp2go.com 2525
Trying 45.33.53.153...
telnet: connect to address 45.33.53.153: Connection refused
Trying 66.228.43.14...
telnet: connect to address 66.228.43.14: Connection refused
Trying 45.79.71.155...
telnet: connect to address 45.79.71.155: Connection refused
Trying 173.255.233.87...
telnet: connect to address 173.255.233.87: Connection refused
失败，因此我不能使用端口2525进行邮件传输。服务器A可以通过25端口远程登录
serverA$ telnet mail.smtp2go.com 25
Trying 45.33.53.153...
Connected to mail.smtp2go.com.
所以我目前正在使用它。
但是当服务器B（与服务器A在同一子网上）可以成功地在端口2525和25上进行远程登录时，这让我很疯狂。A有什么关系？