EMailSender works only with smtp.gmail.com port 465

Projects Networking, Protocols, and Devices
1

By default, EMailSender uses smtp.gmail.com and port 465. That's coded into EMailSender.h.
I tried to use smtp.sendgrid.net, port 25 by calling:

    emailSend.setSMTPServer(smtpServer);
    emailSend.setSMTPPort(smtpPort);

That didn't work -- connect failed.
So then I tried patching the source to use the port and server I wanted. That, too, failed.
My next attempts were to change first the port and then the server. I found that changing either of them caused the connect to fail. The failure seems to be a timeout, since it hangs a while before the failure.

I've tried connecting from a different computer on the same network, and that works, so it doesn't appear to be a firewall problem (I'm using a Firewalla Gold as my firewall).

The system I'm working on is a nano 33 IOT.

Has anyone else seen this problem or been able to use EMailSender to a different smtp server/port?

Thanks,

Ken

2

Are you sure that the selected server accepts requests on port 25? No public mail server uses unencrypted ports these days. Try the same server but port 465

3

It accepts connections. On a local linux box
$ telnet smtp.sendgrid.net 25
establishes a connection just fine.

I've also tried changing just the server and leaving the port as 465. That also fails with the arduino.

5

I was pretty sure that I had, but just tried it again. It fails.

Some more information:

I just looked at my firewall and it shows that 107 B were downloaded and 246 B were uploaded.t
So, it appears that data is being transferred, but the connection is never shown as established. (That's smtp.sendgrid.net port 25)

6

Running tcpdump on my firewall, I see that there is an apparent attempt to do what looks like what might be an SSL handshake at the beginning of the connection. I've tried doing:

    emailSend.setIsSecure(false);

That doesn't seem to solve the problem.
I've tried connecting to a port that expects an encrypted connection, but that didn't work either.

Is anyone else using EMailSender on a nano 33 IOT?