This issue has been caused by recent Microsoft updates on your IT's Email/Exchange/SMTP server.
A workaround for the update is to disable the TLS/SSL in Dimensions:
Click System, Options, System control options
On the System Format tab, next to System Email Defaults, click the Blue arrow.
Click the 2nd button at the top SMTP Servers
Clear the Use SSL check box.
Click Save
Save out of the system options as well.
If the above steps don't resolve the issue, please extend the timeout in ms option in the SMTP Server Settings within Dimensions by carrying out the following steps:
Click the System tab
Settings category
Options button
System Control Option
System Format tab
Under the SMTP Server Settings the Timeout in ms will need to be increased. For example if it is set to 20000000, then it will need to be set to 2147483647.