https://accounts.alibaba.com/register/ifm_reg.htm does not allow "+" in email address. I asked this request be considered and it was not. Your chat support said you do not allow "+" in email address for "security purposes". I do not understand "security purposes" as a valid reason for not considering the request. I am unhappy and I feel a generic answer was given. If I am wrong please let me know with additional information.
The majority of mail servers will deliver "user+tag@domain" to the user "user@domain". Here are just a few of the many mail services that support this gmail.com, outlook.com, and mail.com. You are preventing this feature simply because your web designers did not understand the validation rules of email addresses. We have standards for a reason please consider supporting them correctly.
refs:
https://en.wikipedia.org/wiki/Email_address#Sub-addressing "+" char explained
https://tools.ietf.org/html/rfc5233 ABNF used in RFC documents
