Rules of validating email addresses
A record validation rule checks input to one or more fields is applied when the focus leaves the record.
Usually, a record validation rule compares the values of two or more fields.
When data is entered, Access checks to see whether the input breaks a validation rule – if so, the input is not accepted, and Access displays a message.
Access provides a number of ways to restrict input: You can use these methods of validating data alone or in combination with each other.
Your validation rules can contain expressions — functions that return a single value.
Validation rules can be set in either table design or table datasheet view.For example, a date field might have a validation rule that disallows values in the past. Record Validation Rule You can use a record validation rule to specify a condition that all valid records must satisfy.You can compare values across different fields using a record validation rule.There are three types of validation rules in Access: 1.Field Validation Rule You can use a field validation rule to specify a criterion that all valid field values must meet.
As Sean points out this can leave you open to Do S attacks, but from your description it seems you have a text file rather than a web page, so this shouldn't be a problem.