hi, Does the problem appeared recently? Some things that helped other people: - You need to login via webmail and see whether you exceeded the quota you have. (limit of 500MB by default) - refer to https://www.optus.com.au/for-you/support/answer?id=1434 for the correct settings: mail.optusnet.com.au, port 25, security=none, authentication = password, transmitted insecurely, User Name = part of address before the @. - there is also a conversation at another website, saying that optus might be canceling their e-mail service to some of the domains (search for it, I am not gonna put it here)