AN41: TLS authentication when sending mail over SMTP (HW group products)

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TLS password authentication when sending e-mail over SMTP is becoming a standard.
Some HW group devices support TLS (Transport Layer Security), some do not. This Application Note gives an overview and helps to find a solution.

With ever-growing volumes of spam and increasing numbers of mobile devices, security requirements for mail servers (SMTP) are also rising. Gmail, the leader in freemail service, requires SSL/TLS authentication for sending outgoing mail over their SMTP servers since its beginnings. Other services are starting to follow suit (GMX, Seznam, and others). TLS is thus becoming a standard.

As of early 2015, some HW group devices already support TLS; some devices cannot and will not support it.
Some devices can send email by online portal.

  Supports TLS Number of e-mail recipients SensDesk compatible
Ethernet thermometer / hygrometer
HWg-STE plus
Ethernet thermometer with digital inputs (DI)
Poseidon 2250
SNMP monitoring and data logging
Poseidon2 – entire family
Remote sensor monitoring and I/O control over a LAN
Ares 12/14
GSM thermometer with e-mail (GPRS) and SMS alarms
HWg-PWR 3/12/25
Smart M-Bus to Ethernet gateway
2D water leak detector
Damocles – entire family
Remote I/O monitoring and control over a LAN

Will be supported in Damocles2 (mid-2015)
Full RS-232 serial port to Ethernet with logging
Access control system with monitoring and control over a LAN


What to do if my device doesn't support TLS for outgoing e-mail?

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Spam protection. How many is SIX times six?

To send an e-mail to your “” account, there is no need to send e-mail through Gmail SMTP servers.
Any SMTP server will do. But where to find one?

1) Use the SMTP server of your Internet Service Provider

Your ISP (Internet Service Provider) has a SMTP server – use it. All ISPs provide free SMTP servers for their customers, usually even without any authentication. Security is ensured by allowing access from the ISP's own network only.

2) Set up your own SMTP server

This solution is suitable for corporate clients or for customers with many devices. It is the cleanest solution. However, it does require technical capabilities.

3) Send emails not from the device but from the service

This is solution for HWg-STE plus for example. You do not need SMTP server, send alert emails from your SensDesk account.

4) Send through a SMTP server that is still open

All large e-mail providers are beginning to require TLS authentication for sending out e-mail. However, there are still many small, local services that you can use. Simply set up a dedicated freemail account for your device to send out e-mails.
However, always use one account for each device acting as a single sender. Servers without TLS security often limit the number of devices that can send outgoing e-mail via SMTP.


SMTP server, TLS, e-mail authentication