3.1 KiB
Proposal for mandating lowercasing when processing e-mail address localparts
RFC822 mandates that localparts in e-mail addresses must be processed with the original case preserved. The Matrix spec doesn't mandate anything about processing e-mail addresses, other than the fact that the domain part must be converted to lowercase, as domain names are case insensitive.
On the other hand, most major e-mail providers nowadays process the localparts
of e-mail addresses as case insensitive. Therefore, most users expect localparts
to be treated case insensitively, and get confused when it's not. Some users,
for example, get confused over the fact that registering a 3PID association for
john.doe@example.com doesn't mean that the association is valid for
John.Doe@example.com, and don't expect to have to remember the exact
case they used to initially register the association (and sometimes get locked
out of their account because of that). So far we've seen that confusion occur
and lead to troubles of various degrees over several deployments of Synapse and
Sydent.
Proposal
This proposal suggests changing the specification of the e-mail 3PID type in the Matrix spec appendices to mandate that any e-mail address must be entirely converted to lowercase before any processing, instead of only its domain.
Other considered solutions
A first look at this issue concluded that there was no need to add such a mention to the spec, and that it can be considered an implementation detail. However, MSC2134 changes this: because hashing functions are case sensitive, we need both clients and identity servers to follow the same policy regarding case sensitivity.
Tradeoffs
Implementing this MSC in identity servers would require the databases of existing identity servers to be updated in a large part to convert the email addresses of existing associations to lowercase, in order to avoid conflicts. However, most of this update can usually be done by a single database query (or a background job running at startup), so the UX improvement outweighs this trouble.
Potential issues
Some users might already have two different accounts associated with the same e-mail address but with different cases. This appears to happen in a small number of cases, however, and can be dealt with by the identity server's maintainer.
For example, with Sydent, the process of dealing with such cases could look like:
- list all MXIDs associated with a variant of the email address, and the timestamp of that association
- delete all associations except for the most recent one [0]
- inform the user of the deletion by sending them an email notice to the email address
Footnotes
[0]: This is specific to Sydent because of a bug it has where v1 lookups are already processed case insensitively, which means it will return the most recent association for any case of the given email address, therefore keeping only this association won't change the result of v1 lookups.