SMTP returns 421 Too Many Connections

Yoeri Nijs

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Apr 28, 2024, 2:05:55 PM4/28/24

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Currently working with AWS SES to send transactional email, just fire and forget. My current quota is more than enough:

Daily sending quota
400,000 emails per 24-hour period

Maximum send rate
200 emails per second

However, when I try to send 400 subsequent emails, the F3 SMTP client is throwing a server issue:

Sun, 28 Apr 2024 10:01:20 +0200 https://www.xxx.yyy: 256, 500: SMTP dialog error: 421 Throttling failure: Too many open connection from Account. Try again later.
Sun, 28 Apr 2024 10:01:20 +0200 ([/var/www/html/vendor/bcosca/fatfree-core/smtp.php:162] [/var/www/html/vendor/bcosca/fatfree-core/smtp.php:237] SMTP->dialog() [/var/www/html/vendor/ikkez/f3-mailer/mailer.php:285] SMTP->send() [/var/www/html/app/core/mail/MailSender.php:102] Mailer->send() [/var/www/html/app/core/mail/MailSender.php:44]

I just call the send method and use the true or false return value to handle the process further. What is going wrong here??

Yoeri Nijs

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Apr 28, 2024, 2:06:38 PM4/28/24

to Fat-Free Framework

Important to note here: I already tried to use a sleep to see if I can throttle some things, but this does not help.

Op zondag 28 april 2024 om 20:05:55 UTC+2 schreef Yoeri Nijs:

Yoeri Nijs

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May 9, 2024, 4:43:27 AM5/9/24

to Fat-Free Framework

I think it might have something to do with how F3 is closing smtp connections after sending mails... However, it might also be F3 Mailer, since I use that plugin. Opened an issue for this.

Just a copy-paste of the issue from my side:

The mail plugin causes problems when sending emails in bulk. I use AWS SES and have already adjusted the limits, so AWS should not throw any errors here. However, I still receive smtp errors. It seems that the open connections are not being closed properly.

The error I get:
`SMTP dialog error: 421 Throttling failure: Too many open connection from Account. Try again later. `

I call the F3 mailer by creating an instance and send a mail for every recipient, by doing so:

```
foreach($recipients as $r) {
$mailer = new Mailer();
$mailer->addTo($recipient, null);
...
$mailer->send();
}
```

The number of recipients in my case is +/- 400. I suspect F3 is not closing the connection properly, but just want to make sure it is not the F3 mailer as well.

Op zondag 28 april 2024 om 20:06:38 UTC+2 schreef Yoeri Nijs:

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