Does GMS support either SMTPS or SMTP submission?
GMS supports multiple methods for facilitating the secure transmission of electronic messages over SMTP although SMTP Submission has only been supported in GMS since the release of version 15.02.xx
SMTPS (SMTP over SSL/TLS) is different to SMTP Submission. The former is offered as one of the extended commands supported by Enhanced SMTP (ESMTP) knownn as STARTTLS. This service allows an SMTP client and server to initially communicate over the unsecure port 25 but can then utilise TLS (Transport Layer Security) to provide secure, authenticated communication over the Internet.
It is common practice for ISP’s to block traffic on port 25 in an attempt to reduce the ever increasing volume of spam entering their network. To allow the legitimate sending of mail for their customers, ISP’s often open up the SMTP submission port (default of 587). This will require the sender of the message to first authenticate to the ISP’s mail server in order to be able to send mail through it.
GMS can also provide secure communication over port 465. This is a dedicated secure port so there is no STARTTLS handshaking required. It is also possible for clients to authenticate over this secure channel if required.
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Keywords:smtp smtps port message submission secure authentication tls