SMTP
- swaks – command line SMTP testing tool.
- mailtrap – SMTP server for development.
- Fake SMTP Server for testing
To verify SMTP SPF/DKIM etc are set properly, sent a mail to [email protected], check the reply.
Cloud providers like Amazon AWS, Alibaba, Microsoft Azure, Google Cloud and DigitalOcean do not allow you to run your own mail server. If you need to sent an email from your web application, you need to use one of the Transnational Email Services.
Amazon AWS
How to set Reverse DNS on Amazon EC2. Remove Email Restriction
Amazon EC2
Amazon Lightsail rDNS
Alibaba Cloud
Alibaba Cloud won’t allow SMTP. In case you need an SMTP port, you can request, but it only allows you to send emails using a third-party SMTP server. If you install an SMTP server on your server, Alibaba cloud will permanently disable port 25. For more info, see
https://www.alibabacloud.com/help/faq-detail/56130.htm
If your site needs to send an email, use DirectMail, transactional email service provided by Alibaba Cloud
Google Cloud
https://cloud.google.com/compute/docs/tutorials/sending-mail/
Microsoft Azure
DigitalOcean
They only allow SMTP after 60 days of use to avoid spam. Source: See pinned answer by alexdo
Vulr
Vultr blocks the SMTP port by default.
https://www.vultr.com/docs/what-ports-are-blocked
You need to fill out the form below to unblock the SMTP port.
https://my.vultr.com/billing/unblock_smtp_port/
Linode
SMTP is blocked by default. To unblock, create A record + rDNS for the hostname. Then open a support ticket at