[BUG] Slack service messaging error parsing message "3.1.8.JBO"

I tested my guessing and here is

echo "##teamcity[notification notifier='slack' message='3.1.8.JB' sendTo='teamcity' connectionId='PROJECT_EXT_5']"

and got

Slack notifier: Found external domains that are not allowed by configuration: [3.1.8.JB]. Will not send Slack notification.

I think this is because JB somewhere reserved as JetBrains reverence in the URL or something like that.

But for example 

echo "##teamcity[notification notifier='slack' message='JB' sendTo='teamcity' connectionId='PRO0JECT_EXT_5']"

OR

echo "##teamcity[notification notifier='slack' message='JB.1.1.1' sendTo='teamcity' connectionId='PROJECT_EXT_5']"

works properly