What exactly is an alias?
Every mailbox in Microsoft 365 has one primary address. On top of that you can add extra addresses, called aliases. All email sent to an alias arrives in the same mailbox as the primary address, so the recipient still has just one inbox. An alias needs no extra licence, because no new mailbox is created.
Typical examples in an SME:
- A second domain. You have a new company name or an extra domain name, and email to the old address must keep arriving.
- Name variants. Both j.jansen@ and jan@ should reach the same person.
- A general address for one person. For example quotes@ that only the owner reads.
An alias on an extra domain only works when that domain has been added and verified in Microsoft 365. Also make sure the domain's DNS records are correct, or email won't arrive or your sent email ends up as spam.
Adding an alias
An admin adds an alias in the Microsoft 365 admin center on the user, or in the Exchange admin center under Recipients > Mailboxes. There you pick the mailbox and manage the extra addresses under Email addresses. The address shown in bold is the primary address, also called the default reply address. To add several aliases at once, you can also use PowerShell and a CSV file.
Replying and sending from an alias
This is where things often go wrong. By default, Exchange Online rewrites an alias to the primary address. A customer who emails your old address therefore gets a reply from the primary address. Usually that's fine, but not when you deliberately want to use a separate address externally.
Microsoft has an organisation-wide setting for this: sending from aliases. An admin turns it on with PowerShell. After that the alias is kept, and staff using recent versions of Outlook can choose which address they send and reply from. Note that this setting applies to all email of all mailboxes, so even users without a new Outlook may notice a difference. Test it first and tell your staff what's changing.
Plus addresses: handy for sign-ups
With plus addresses you add your own label to your address, such as name+supplier@ followed by your own domain name. Email to that address simply arrives in your own mailbox. This is on by default in Exchange Online and needs no setup. You can see straight away which website or supplier a message came through, and an Outlook rule can move that email to a folder automatically.
Plus addresses do have limits. You can't send from them, and some websites don't accept the plus sign. If your organisation doesn't want plus addresses, an admin can turn them off in the Exchange admin center under Settings > Mail flow.
When an alias isn't the right choice
- Several people need to read along. If info@ or invoices@ is handled by a team, use a shared mailbox. Everyone then has the same inbox and you can see who answered what.
- Just forwarding email to a group. If an address must reach several people at once, a distribution list or Microsoft 365 group fits better.
- Someone leaves the company. If important aliases sit on a departing colleague's mailbox, move them deliberately to another mailbox or a shared mailbox. Otherwise they disappear along with the account.
How Floor ICT handles this
Floor ICT lists which addresses you use and what for. We add the aliases to the right mailbox, check that extra domains are verified and that SPF, DKIM and DMARC are correct. If you want to send from an alias, we test that first before turning it on for everyone. That way all email arrives, you don't pay for unnecessary mailboxes and everyone replies from the right address.