Email was not there at all - not in searched results nor in mailbox history. Only reference was seen in firefox browser history where url to maiblox is kept + tab description (fortunately it included reservation id). Url did not resolved into showing email content.
Depending what RF is being used for, Selenium may be under the hood wrapped in multi-layers of keywords. In other cases, where testing is not web/REST based (protocol testing, HW testing), what is being used for executing logic is up to devs/testers.
My working theory is that in old times phones had rotary dial instead of key pad. Number 1 was the longest to dial, 9 was the shortest (as I remember from childhood days). Thus, fastest way to dial 3 digit code was to use numbers with as much as 9 as possible (997,998,999).