Account is the "local-part" of the email address and can contain letters, numbers, and periods.
Password must be at least 8 characters with 12 or more being highly recommended.
The password must contain characters from at least three of the following four groups:
Lower Case Letters, Upper Case Letters, Numbers, Punctuation/Special Characters.
Status can be used to temporarily disable the email account. If the account is enabled with the Admin option they can managed all email accounts.
Quota is the storage limit in GB for the email account.
Rate Limit is the hourly sending rate limit for the email account, and is multiplied by 10 for the daily sending limit.
Filtering should normally be left at Junk & Spam. Junk only disables Spamassassin, and None disables additional checks like SPF, DKIM & DNS Blacklists.