Invalid Characters for MailBoxes There a few reserved characters that can not be used in the creation of mailboxes. The Characters that are not allowed are '& . - _' also the creation of a mailbox with 8-bit character sets. Some Quotes from the RFC 3501. 5.1. Mailbox Naming Mailbox names are 7-bit. Client implementations MUST NOT attempt to create 8-bit mailbox names, and SHOULD interpret any 8-bit mailbox names returned by LIST or LSUB as UTF-8. Server implementations SHOULD prohibit the creation of 8-bit mailbox names, and SHOULD NOT return 8-bit mailbox names in LIST or LSUB. See section 5.1.3 for more information on how to represent non-ASCII mailbox names. Note: 8-bit mailbox names were undefined in earlier versions of this protocol. Some sites used a local 8-bit character set to represent non-ASCII mailbox names. Such usage is not interoperable, and is now formally deprecated. The case-insensitive mailbox name INBOX is a special name reserved to mean "the primary mailbox for this user on this server". The interpretation of all other names is implementation-dependent. In particular, this specification takes no position on case sensitivity in non-INBOX mailbox names. Some server implementations are fully case-sensitive; others preserve case of a newly-created name but otherwise are case-insensitive; and yet others coerce names to a particular case. Client implementations MUST interact with any of these. If a server implementation interprets non-INBOX mailbox names as case-insensitive, it MUST treat names using the international naming convention specially as described in section 5.1.3. There are certain client considerations when creating a new mailbox name: 1) Any character which is one of the atom-specials (see the Formal Syntax) will require that the mailbox name be represented as a quoted string or literal. 2) CTL and other non-graphic characters are difficult to represent in a user interface and are best avoided. 3) Although the list-wildcard characters ("%" and "*") are valid in a mailbox name, it is difficult to use such mailbox names with the LIST and LSUB commands due to the conflict with wildcard interpretation. 4) Usually, a character (determined by the server implementation) is reserved to delimit levels of hierarchy. 5) Two characters, "#" and "&", have meanings by convention, and should be avoided except when used in that convention. 5.1.3. Mailbox International Naming Convention Server implementations SHOULD verify that any mailbox name with an embedded "&" character, used as an argument to CREATE, is: in the correctly modified UTF-7 syntax, has no superfluous shifts, and has no encoding in modified BASE64 of any printing US-ASCII character which can represent itself. However, client implementations MUST NOT depend upon the server doing this, and SHOULD NOT attempt to create a mailbox name with an embedded "&" character unless it complies with the modified UTF-7 syntax