I have a problem with SNMP communty strings on the UTM

It *may* be an input sanitization in the gui/web interface.  Have you tried via command line by chance?  I've no idea what the command would be, though.

The help says the following so it seems to be by design:

Select allowed networks.

Networks listed in the Allowed Networks box are able to query the SNMP agent running on Sophos UTM. You should only add networks to the Allowed Networks that will query the SNMP agent, it is not advisable to add any none private networks to the list. Note that the access is always read-only.

• Community string: When using version 2, enter a community string. An SNMP community string acts as a password that is used to protect access to the SNMP agent. By default, the SNMP community string is "public", but you can change it to any setting that best suits your needs.

  Note – Allowed characters for the community string are: (a-z), (A-Z), (0-9), (+), (_), (@), (.), (-), (blank).

• Username/Password: When using version 3, authentication is required. Enter a username and password (second time for verification) to enable the remote administrator to send queries. The password must have at least eight characters. SNMP v3 uses SHA for authentication and AES for encryption. Note that username and password are used for both of them.

thanks for this, very helpful.

funny how all the other routers/firewall/switches don't have this issue.

you learn something new everyday :)