Learn more about the Sendmail Virtusertable feature. Our Sendmail Support team is here to help you with your questions and concerns.

Sendmail Virtusertable | A Quick Peek

Did you know that Sendmail comes with a useful feature known as virtusertable?

It acts as a database, mapping virtual domains into new addresses. In short, it offers a unique way to reroute mail delivery without changing mail headers.

Today, we are going to take a closer look at virtusertable, exploring examples, configurations, and key differences from other mail mapping mechanisms.

Virtusertable lets us map virtual domains to alternative addresses. It operates as a database hook into the early stages of the parse rule set 0. Then redirects mail delivery based on predefined mappings. Importantly, it does not modify mail headers, making it an ideal solution for fine-tuning mail routing.

For example, consider the following mapping in a virtusertable source text file:

contact@sales.store.com   inquiries
order@sales.store.com      processing@remote.host
support@auctions.com       processing@remote.host
@fantasymarket.com         user@another.market


Here, the first three lines display a full address for the key, redirecting to either a local or remote user. The first line will be delivered to a local user (inquiries), the second and third to a remote user (processing@remote.host). The fourth line displays how all mail to a virtual domain (`f@fantasymarket.com`) can be directed to a single address (`user@another.market`), irrespective of the user part.

Furthermore, Sendmail allows multiple lookups. This enables one line to reference another. For instance:


contact@sales.store.com    forsale@fantasymarket.com
@fantasymarket.com         user@another.market


In this case, mail to `contact@sales.store.com` will be delivered to `user@another.market`.

Handling Errors

Virtusertable can handle errors by using the `error:` value.

For example:


info@sales.store.com error:nouser We no longer sell things here (V8.9 and earlier)
info@sales.store.com error:5.7.0:550 We no longer sell things here (V8.10 and above)


The text after `error:` is passed to the `#error` delivery agent, allowing customized error messages.

Configuring Virtusertable

To declare virtusertable in our mail configuration file, we can use:

FEATURE(`virtusertable')

This results in the database declaration:

Kvirtusertable hash /etc/mail/virtusertable

If you prefer a different database type or location, provide an argument:

FEATURE(`virtusertable',`dbm -o /etc/mail/virt_user_table')

Furthermore, Virtusertable supports LDAP. We can specify it as a second argument:

FEATURE(`virtusertable', `LDAP')

This will generate the default LDAP configuration. This offers flexibility in our mail setup.

At the end of the day, Virtusertable in sendmail helps fine-tune mail delivery.

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Conclusion

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