CRM 2011 Email Router issue Pending Send

Good afternoon,

We are having an issue related to the sending of e-mail, which remains in the status "Pending Send".

Explanation:

Currently, around 10,000 thousand emails are sent daily, after a period of time the emails begin to accumulate, 
generating a high number of emails in the status "Sending Pending", thus delaying the notification to the applicants, 
receiving the emails emails after hours of delays.

When accessing the log on the e-mail router server, the following error message is displayed:

#14494 - A provider work item using assembly: Microsoft.Crm.Tools.EmailProviders.dll and 
class: Microsoft.Crm.Tools.Email.Providers.SmtpPollingSendEmailProvider aborted because it was running longer than allowed. 
This behavior can occur when there is a problem with the network or because the mail server is busy. 
Verify that you can log on to the email server using an email application that uses the account specified for the Email Router.

We have already restarted the email sending service on the server and it remains the same, 
at the end of the day the amount of email is high.