Email validation in "form" entry

Hi - Sorry if this is elsewhere. I'm getting some respondents emailing me to say that the survey isn't accepting their @gmail email addresses. I'm asking for emails via the "form" format question. Then in the option tabs for the email line, I had selected "Validation: Valid email address". This is an option *within* the question, and I hadn't set any validation on the toolbar on the right (outside the question in the survey builder, if that makes sense). Is there any reason why these settings would prevent particular domain names being accepted? For now I've turned off validation on this line until I find a fix. Thank you :)