Problem sending multiple e-mails via SMTP

[beparrish]

I have a Verizon.net account using DSL. I use an applicaiton that gives me the ability to send e-mails to multiple recipients. The program loops through the recipients, builds a unique e-mail just for then, and then sends the e-mail.

The application is sending the e-mail to smtp.verizon.net using SSL and Port 465. I also suppy my valid Verizon username and password.

After the first 10 e-mails are sent (within 4-5 seconds), the Send process begins failing sporadically, returning an error message like the following:

421 Connection from xx.xxx.xxxx.xx not accepted at this time

What would cause smtp.verizon.net to reject these connection attempts ??

[PJL]

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@beparrish wrote:

I have a Verizon.net account using DSL. I use an applicaiton that gives me the ability to send e-mails to multiple recipients. The program loops through the recipients, builds a unique e-mail just for then, and then sends the e-mail.

The application is sending the e-mail to smtp.verizon.net using SSL and Port 465. I also suppy my valid Verizon username and password.

After the first 10 e-mails are sent (within 4-5 seconds), the Send process begins failing sporadically, returning an error message like the following:

421 Connection from xx.xxx.xxxx.xx not accepted at this time

What would cause smtp.verizon.net to reject these connection attempts ??

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It could be that the messages are being sent too quickly as single connection events rather than in one send connnection, and Verizon is limiting the connnection because too many connections requests in a short amount of time can be a denial of service attack on the Verizon server or spam.  Hotmail does the same thing if a connection request is sent too often from a given IP address. 

[beparrish]

Thanks for the response. That's what I was thinking, that there was some sort of throttle in place. I spent over 3 hours on the phone with Verizon support today, and they were unable to offer any explanation why, after going through the SSL client handshake and establishing the SSL channel the connection request would not be accepted by their SMTP server.

DATE: Wed, 6 Nov 2013 14:14:13 -0500
start to connect smtp.verizon.net 465 ...
start to connect 2, 1, 0, 0x00000000
connected
[SSL]start to initialize security library
[SSL]start to create client credentials
[SSL]start to enable direct SSL
[SSL]client handshake
[SSL]verify server certificate
[SSL]SSL channel established
421 Connection from 75.151.203.233 not accepted at this time
[SSL]Error 0x00090317 returned by DecryptMessage, Data size 29
connect failed

I've modified our process so it "sleeps" for two seconds after an e-mail is successfully sent, but I still encounter the failure. I suspect that I'm going to have to advise our clients that using Verizon's SMTP server is not going to be an option going forward.

[PJL]

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@beparrish wrote:

Thanks for the response. That's what I was thinking, that there was some sort of throttle in place. I spent over 3 hours on the phone with Verizon support today, and they were unable to offer any explanation why, after going through the SSL client handshake and establishing the SSL channel the connection request would not be accepted by their SMTP server.

DATE: Wed, 6 Nov 2013 14:14:13 -0500
start to connect smtp.verizon.net 465 ...
start to connect 2, 1, 0, 0x00000000
connected
[SSL]start to initialize security library
[SSL]start to create client credentials
[SSL]start to enable direct SSL
[SSL]client handshake
[SSL]verify server certificate
[SSL]SSL channel established
421 Connection from 75.151.203.233 not accepted at this time
[SSL]Error 0x00090317 returned by DecryptMessage, Data size 29
connect failed

I've modified our process so it "sleeps" for two seconds after an e-mail is successfully sent, but I still encounter the failure. I suspect that I'm going to have to advise our clients that using Verizon's SMTP server is not going to be an option going forward.

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I doubt two seconds is sufficient, but that's just a guess.