using nextcloud as an email client -> Email sent to [email protected] contains non reverse-alias addresses

[ehrt74]

hello! i'm trying to get the service working with the email software on nextcloud. i have nextcloud configured to fetch the mail from my email account. when i respond to a mail forwarded by simple-login, simple-login doesn't forward the mail sayint that my response contains non reverse-alias addresses. am i running afoul of https://simplelogin.io/docs/getting-started/compatibility-email-alias/ ? does anybody know a way around this? when i respond using the webmail of my email provider simple-login works fine :)

many thanks in advance.

okay, i now have some examples of the headers of the emails, which i got from the webmail of my email provider

this is what the email sent from next cloud looks like in the sent folder of my email provider (this one gets rejected by simplelogin):

From: me [email protected]
To: "the alias" [email protected]
Cc:
Subject: mi testas denove
Message-ID: 20260210210402.Horde.cXLPjG_b-p2riNKb8IM6wjs@localhost
User-Agent: Horde Application Framework 5
Date: Tue, 10 Feb 2026 21:04:02 +0000
Content-Type: text/plain; charset=utf-8
MIME-Version: 1.0

and this is what gets sent if i reply directly using the web-client of my email provider (simplelogin sends this one on):

MIME-Version: 1.0
Date: Tue, 10 Feb 2026 22:08:19 +0100
From: [email protected]
To: "the alias" [email protected]
Subject: Re: simplelogin testo
In-Reply-To: [email protected]
References: [email protected]
Message-ID: [email protected]
X-Sender: [email protected]

the exact reply from simplelogin for the first mail is:

Your email sent to [email protected] from [email protected] (Re: simplelogin testo) contains an address
which isn't a reverse-alias in the To: or Cc: field.

The email was then directly sent to this recipient and doesn't pass by SimpleLogin.
Unfortunately, it reveals your real mailbox address to the recipient.
Please create a reverse alias for each recipient to make sure your mailbox stays hidden and re-send the email.

i find this odd, because the To: field is for both mails the same, and there is entry in the Cc: field of the first email. Maybe that is the problem?does simplelogin not forward the email because the Cc: field is specified but empty?

that's it! if i add [email protected] as a Cc: explicitly, then simplelogin forwards the mail.
so it looks like there are 2 ways forward:

1. find a way to stop nextcloud adding an empty Cc: field or
2. ask the nice people at simplelogin to change the software so it ignores empty Cc: fields (or add a configuration option)