I have a system that sends out emails and queues them if volume increases.
If it's 1 or 2 emails per hour, it sends out fine.
On busier times, the queue gets backed up and soon email sending starts to fail.
I've load-tested the SMTP server from my local - no problems there.
However, when I try to do the load-test from my EC2 server
- which is in a private subnet of a VPC
- where outgoing traffic goes through a NAT
- and where we've set up our own DNS server
the first few go out fine - and the rest starts to throw errors.
Here's the C# exception ToString()
System.Net.Mail.SmtpException: Failure sending mail. ---> System.Net.WebExcept
ion: Unable to connect to the remote server ---> System.Net.Sockets.SocketExcept
ion: A connection attempt failed because the connected party did not properly re
spond after a period of time, or established connection failed because connected
host has failed to respond [SMTPServerIP]:25
at System.Net.Sockets.Socket.DoConnect(EndPoint endPointSnapshot, SocketAddre
ss socketAddress)
at System.Net.ServicePoint.ConnectSocketInternal(Boolean connectFailure, Sock
et s4, Socket s6, Socket& socket, IPAddress& address, ConnectSocketState state,
IAsyncResult asyncResult, Exception& exception)
--- End of inner exception stack trace ---
at System.Net.ServicePoint.GetConnection(PooledStream PooledStream, Object ow
ner, Boolean async, IPAddress& address, Socket& abortSocket, Socket& abortSocket
6)
at System.Net.PooledStream.Activate(Object owningObject, Boolean async, Gener
alAsyncDelegate asyncCallback)
at System.Net.PooledStream.Activate(Object owningObject, GeneralAsyncDelegate
asyncCallback)
at System.Net.ConnectionPool.GetConnection(Object owningObject, GeneralAsyncD
elegate asyncCallback, Int32 creationTimeout)
at System.Net.Mail.SmtpConnection.GetConnection(ServicePoint servicePoint)
at System.Net.Mail.SmtpTransport.GetConnection(ServicePoint servicePoint)
at System.Net.Mail.SmtpClient.GetConnection()
at System.Net.Mail.SmtpClient.Send(MailMessage message)
--- End of inner exception stack trace ---
at System.Net.Mail.SmtpClient.Send(MailMessage message)
at ConsoleApplication2.Program.Main(String[] args) in c:\ConsoleApplication2\
Program.cs:line 49
I'm pretty sure it's not a code issue - most likely a setting on the NAS or DNS. Can someone point me in the right direction?
