The e-mail address field on Customer Portal has validation rule, and throws error message if the text input do not follow this rule.
Currently this field limits the number of text after @(atmark) followed by .(dot) with 4 digits. We encountered e-mail addresses with domain name "@oguchiganka.tokyo" which has 5 digits and could not onboard via MARLO portal.
Please increase the number of digits to not block user registration journey.