Struggling with email

Hello Everyone,
Once again I am struggling with emails.
14 days ago all emails were being delivered without any error, but now none of the email is delivered neither from local site nor from hosted site.
I did not change any single letter of code in web.config and in pages.

Web config file is as follows.
<appSettings>
<add key="MailFromAddress" value="<user name>@gmail.com"/>
<add key="MailToAddress" value="<user name>@gmail.com"/>
<add key="SenderName" value="Jack"/>
<add key="ReceiverName" value="Jack"/>
<add key="SendMailOnError" value="true"/>
</appSettings>

and under system net
<system.net>
<mailSettings>
<smtp from="Jack &lt;<user name>@gmail.com&gt;" deliveryMethod="Network">< ...