Hi,
Increasing a quota for just a single user is not possible. You usually have an over-arching quota (20MB in your case) and restrict quotas down for individuals. If the user wants to send 50MB I suggest you tell them to put the file on a ftp/http site, or split the attachment into smaller chucks using winzip or similar and email that way.
Increasing quota is a slippery slope. Once you increase it to 50MB, you will get request to increase it more, and more and more etc. The problems start to arise when the user is sending a large email to an external address which doesn't accept large emails (and you tend to get blamed for that being the 'email guy') or if they send to a mailing list or when they get bounces which cause their account to go overquota.
Regards,
Shane.
Let's make some definitions, so we don't confuse anybody.
"quota". limit on maximum size of all mail in your mailbox
"max received mail size". Maximum size of one message.
While you can indeed change the size of an INDIVIDUAL's quota, quite easily, I don't think that is that this poster is asking for.
There is an ldap attribut that may be helpful. I have not tested, nor can I find much in the way of documentation about it:
LDAP_BLOCKLIMIT