我认为这可能意味着您发送了一个空白行到smtp服务器。

确保您的命令中没有任何命令行。

您可以记录事务并粘贴日志的副本？

在这里查看有关记录
http://swiftmailer.org/docs/logger-plugin

I am using gmail as an smtp server for my swiftmailer class.

however I am getting

Expected response code 220 but got code "", with message "" in "\classes\Swift\Transport\AbstractSmtpTransport.php"

What does this mean?

I think it probably means you sent a blank line to the smtp server.

Make sure none of your commands have line feeds in them.

Can you log the transaction and paste a copy of the log?

see here for details about logging http://swiftmailer.org/docs/logger-plugin