Looks like this function has exactly the same behavior as base64_decode($test, true) -> it returns FALSE if $text contains characters outside the Base64 alphabet, although this isn't documented here.
(PHP 4, PHP 5)
imap_base64 — Decode BASE64 encoded text
string imap_base64 ( string $text )
Decodes the given BASE-64 encoded text.
The encoded text
Returns the decoded message as a string.
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