How to Send Email on Behalf of Someone Else or a Shared Address

An assistant sends for a director, a teammate answers as support@, an agency sends as its client. There are three ways to do this and only one of them looks right to the recipient and passes authentication. This guide explains From, Sender and Reply-To, how to set up a send-as identity in each mail app, and the trap that gets on-behalf mail rejected.

Quick summary

• From: who the message is from. This is what recipients see and what DMARC checks. Sending as support@yourdomain.com means From is support@.
• Sender: who actually pressed send when it differs from From. Some apps show "Ana on behalf of Support". Optional and rarely needed for small teams.
• Reply-To: where replies should go if not to From. Useful when a system sends but a person should receive answers.
• Create the shared address as a real mailbox, for example support@yourdomain.com. On OquMail it is one of the 15 free mailboxes.
• Add it to your mail app as a second account with its own password: IMAP mail.oqumail.com port 993 SSL/TLS, SMTP mail.oqumail.com port 587 STARTTLS.

Three headers, three meanings

• From: who the message is from. This is what recipients see and what DMARC checks. Sending as support@yourdomain.com means From is support@.
• Sender: who actually pressed send when it differs from From. Some apps show "Ana on behalf of Support". Optional and rarely needed for small teams.
• Reply-To: where replies should go if not to From. Useful when a system sends but a person should receive answers.

Option 1: send as a shared mailbox (cleanest)

1. Create the shared address as a real mailbox, for example support@yourdomain.com. On OquMail it is one of the 15 free mailboxes.
2. Add it to your mail app as a second account with its own password: IMAP mail.oqumail.com port 993 SSL/TLS, SMTP mail.oqumail.com port 587 STARTTLS.
3. When composing, pick the support@ account in the From dropdown. The message is authenticated as support@, lands in the shared Sent folder, and replies come back to the shared inbox where colleagues can see them.

Option 2: add the address as an identity on your own account

• Thunderbird: Account Settings, Manage Identities, Add. Set the address, name and signature; keep the same outgoing SMTP server.
• Apple Mail: Mail, Settings, Accounts, choose the account, and in the Email Address field add the extra address separated by a comma.
• Outlook desktop: File, Account Settings, add the shared mailbox as a separate account, or use the From button in a new message and type the address. Outlook will send it if the server allows that mailbox to use the address.
• Gmail routing your domain: Settings, Accounts, Send mail as, and enter the SMTP details above.
• Sending as an identity works only when the server permits that mailbox to use the address, usually because it is an alias on the same mailbox or the same domain. Sending as a completely different domain from your own account fails DMARC.

Sending for a person, not a role

An assistant sending as the director's own address is common but risky: the director's Sent folder does not show it unless the assistant uses the director's account, and a reply may reach the wrong person. The better pattern is a From of the director's address with Reply-To set to the assistant, or simply the assistant writing from their own address with "on behalf of" in the signature. If the assistant needs to genuinely act as the director, give them the director's mailbox in their mail app as a second account with a shared password, and rotate it when the arrangement ends.

The DMARC trap

• If From is client.com but the mail is sent through your own host with your own DKIM signature, the client's DMARC policy sees an unaligned message. With p=reject, it never arrives.
• To send legitimately as another company, that company must either give you a mailbox on their domain, or add your sending host to their SPF and set up DKIM for it.
• The same applies to CRMs and booking tools that send "from" your address: they need your domain's DKIM or they must use your host's SMTP or API.

Using the API for system mail

POST https://api.oqumail.com/api/v1/emails
Authorization: Bearer oqm_live_xxxxxxxxxxxxxxxx
Content-Type: application/json

{
  "from": "Support at Yourcompany <support@yourdomain.com>",
  "to": "customer@example.com",
  "subject": "Re: your question about delivery",
  "html": "<p>Hi, Ana here from the support team...</p>"
}

Common questions

Will the recipient see who actually sent it?

Only if your app adds a Sender header, which Outlook does for "send on behalf" permissions and most other apps do not. With a shared mailbox as a second account, the message looks like it came from support@ and nothing else.

Where do replies go?

To the From address unless Reply-To is set. That is why sending as a shared mailbox is better than sending from a personal address with the shared one in CC: replies return to the shared inbox by default.

Can I send as a colleague from my phone?

If the colleague's or shared mailbox is added to the phone as an account, yes. iOS Mail and Outlook mobile let you pick the sending account when composing. If only your own account is on the phone, an alias listed in that account can be chosen, but a different mailbox cannot.