I’ve been using this style of catch-all address for years. I’ve never had to explain, and have only once had an issue with it, last year when I scheduled an appointment with a business that I’ll call Alpha Beta Gamma, and they rang me a few minutes later saying they couldn’t confirm the appointment properly because their system was objecting to the email address I’d provided, which was alphabetagamma@, and maybe that was because of their business name being in it, so could we try something else, like abg@ (yes, they made the suggestion), and that worked.