Update read Me

Fixed: the bug that prefix each attachment filename with message id.

Fixed: the error of that copy attachments of one mail to another if they are processed at the same time.

Fixed: the code to use content id instead of sequence when resolving CID of inline enbeded attachment images.
This fix issues that happen when there are both attachments and embeded images.

New: Support granting sending permission for each mailint list seperately.

New: Allow multiple whitelisted senders to post to list on behalf of a list owner without having list owners credentials.

Use same machanism that phplist uses to download atachments. Using a file similer to dl.php.
In fact the new file dl_mailtolist.php is a copy of dl.php with some tiny changes.
If needed these changes can directly placed inside dl.php.

Files Modified:
- get_email.class.php
- main.php
New File
- dl_mailtolist.php - this is a modified version of dl.php from phplist.