Email is not being sent consistently in Kentico. No Errors in error log and those mail does not show

Hi All, We are facing currently some weird issue in Production environment. We are seeing some mails are not being sent consistently. It is sending 60% of mail, but skipping few of the mails with same code being executed. Don't know what's going wrong over here. I have put extra logging in mail code as info logging to record each and every steps it is executing. Just wanted to compare success versus failure events occurred. Surprisingly all the event data is same whether mails is being sent or it is not sent. It does not have any exception or any steps skipped if mail is not sent. I have looked into CMS_EMAIL table to just check if it has missed to show mail on UI email queue. Surprisingly it does not contain any record for that email.

With this findings i tried to look the kentico Sendmail method. I drilled down kentico code using resharper in MailNotification class EmailSender.SendEmail(siteName, emailMessage, true); method. Kentico internally starts separate thread to send the mail, Actual method which sends mail is as bellow and it has code that absorbs the ThreadAbortexception which we could not record. This could occur in SMTP server, these code we do not have access and it is just DLLs we are using from Kentico. This is the probable cause I can think of as of now, Let me know if any of the way you can help us out to drill down the issue further. Thanks in advance.

       private void Run()
{
WindowsImpersonationContext impersonationContext = (WindowsImpersonationContext) null;
try
{
impersonationContext = this.identity.Impersonate();
bool flag = this.emailsToSend == EmailMailoutEnum.OnlyAppQueue;
if (this.emailQueueApp.Count > 0)
this.ProcessQueue();
if (!EmailHelper.IsAnySendingEnabled() || flag)
return;
if (this.emailIds.Length > 0)
this.SendSpecific();
else
this.SendFromQueue();
this.mailoutComplete.WaitOne();
this.ProcessPendingMassEmail();
}
**catch (ThreadAbortException ex){}**
catch (Exception ex)
{
EventLogProvider.LogException("EmailEngine", "ThreadSender", ex);
}
finally
{
this.Init();
impersonationContext.Undo();
}
}