Check E-mail or text field for special word

Hello,
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I want to create a joomla registration for my website.But I want that only company members are allowed to register.I came up with two options for this: either you register with a company email address or there is a code that has to be entered if you do not use a company address.Can someone help me make this happen?
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Best regards,
Lampi

you can use the "Regular expression" or "Contains" rules of the validation to check for specific email domain or word!

thank you i will try this