Postclient

Language: English · Italiano · Français · Deutsch · Español

The application UI is English or Italian. These documents describe the same client for people who use certified electronic mail (Italian PEC and eIDAS REM) as private users or as a practice / agency.

Postclient is a desktop mail client for Windows, Linux, and macOS (Apple Silicon and Intel). It connects with IMAP, POP3, and SMTP to mailboxes you already have: ordinary mail, Italian PEC at a qualified gestore, and European REM (registered electronic mail) when the operator publishes IMAP/SMTP.

It is not a qualified trust service provider (QTSP), not a PEC operator, not a timestamp authority, and not a cloud mailbox. Receipts and transport envelopes come from the gestore / QTSP. This client unwraps them, shows the operator’s evidence, and keeps a copy on the machine.

Kind	Desktop mail client
OS	Windows, Linux, macOS
Stack	C#, .NET 10, Avalonia, MailKit
License	Apache 2.0
Not	A QTSP, a new PEC/REM address, hosted mail, or a scanner

Changes: CHANGELOG.md. Contributing: CONTRIBUTING.md.

Who it is for

Private individuals

Use it as the daily client for one or more addresses: Gmail or Microsoft 365 next to a personal PEC (Italy) or an IMAP REM mailbox (EU). Mail is indexed on this PC so you can search a condominium notice, a tax file, or a PA communication years later without leaving the originals on someone else’s server.

Typical private use: keep the certified mailbox and the ordinary mailbox in one window; see whether a PEC was accepted and deposited; print or save a PDF of a message; export the original .eml if a municipality, bank, or court asks for it.

Practices and agencies

Use it when several certified identities must not be mixed: personal PEC, studio PEC, and ordinary mail (Gmail / Microsoft 365). From is a picker of connected mailboxes, not a free-typed address. A commercialista, avvocato, notaio, CAF, condominium administrator, or EU practice that files with PA can:

• keep each gestore mailbox separate, with its own IMAP quota in the status bar;
• label messages on this PC by practice (for example a condominium or a client file) — labels are local, not a shared studio database;
• group a send with the gestore ricevute that refer to it;
• export selected originals as a fascicolo of .eml files for a notaio, a court, or a PA desk;
• open FatturaPA XML attachments as a readable view (XML parser, not AI);
• import a colleague’s Thunderbird profile or an Outlook PST/OST without installing Outlook.

The program does not replace the gestore, does not issue a qualified ricevuta, and does not share the practice table across the office.

Accounts and protocols

Incoming: IMAP (full folder tree) or POP3 (Inbox only). Outgoing: SMTP. Encryption: Auto, SSL/TLS, STARTTLS, STARTTLS if available, or none. MailKit uses the SASL methods the server advertises.

Several mailboxes can be stored at once. Presets fill hosts and ports:

Preset	Role
Gmail	IMAP/SMTP; sign in with Google (OAuth2 / XOAUTH2) or a Gmail app password
Outlook / Microsoft 365	IMAP/SMTP; sign in with Microsoft. Most of these accounts reject a mailbox password
IT PEC — Aruba	imaps.pec.aruba.it / smtps.pec.aruba.it (POP3: pop3s.pec.aruba.it)
IT PEC — InfoCert Legalmail	mbox.cert.legalmail.it / sendm.cert.legalmail.it. Username is often the InfoCert User ID, not the address
IT/EU PEC — Namirial	imaps.sicurezzapostale.it / smtps.sicurezzapostale.it
IT PEC — Poste Italiane	mail.postecert.it
IT PEC — Register.it	imap.pec-email.com / smtp.pec-email.com
IT PEC — Libero	mail.postacert.it.net
EU — Intesi Group	imap.ig-trustmail.com / smtp.ig-trustmail.com
IMAP / POP3	Any other host the operator gave you

Certified IMAP mailboxes use the gestore password, or an app password if the gestore has 2FA. AR24 (France), De-Mail (Germany), IncaMail (Switzerland), and Lleida (Spain) are usually not IMAP. If that operator gave you IMAP/POP3 hosts, choose IMAP / POP3 and enter them. Otherwise this client cannot open that mailbox; it can still display ETSI REM evidence on messages you import as .eml.

OAuth needs a Google client ID (ends with .apps.googleusercontent.com) and, for Web clients, the client secret — paste both in Account Settings (the secret is stored in secrets.bin, not as the mailbox password). Desktop public clients need no secret. Environment variables POSTCLIENT_GOOGLE_CLIENT_ID / POSTCLIENT_GOOGLE_CLIENT_SECRET are also accepted. Enable the Gmail API, add scope https://mail.google.com/ on the consent screen, allow loopback http://127.0.0.1, and enable IMAP in Gmail. Microsoft: Azure Application (client) ID (a GUID); public client; redirect http://localhost; IMAP/SMTP permissions.

Passwords and OAuth refresh tokens stay next to settings (DPAPI on Windows, file mode 600 on Linux/macOS), never in settings.json.

Italian PEC

Italian certified mail is a busta (envelope) produced by the gestore:

• transport message with X-Trasporto: posta-certificata, daticert.xml, and the original as postacert.eml;
• ricevute (X-Ricevuta) in Inbox and Ricevute: accettazione, presa-in-carico, avvenuta-consegna, non-accettazione, mancata-consegna, rilevazione-virus, preavviso-errore-consegna.

View → Unwrap PEC/REM envelope shows the inner postacert.eml (the message the recipient was meant to read) instead of the outer gestore wrapper. The Type column marks PEC (transport) or RIC (ricevuta).

Italian PEC has no read receipt. Avvenuta consegna means the message was deposited in the recipient’s certified mailbox, not that a person opened it.

European REM (eIDAS)

When the message carries ETSI REM evidence (REMEvidence / urn:etsi:rem, or a part name such as remevidence / rem-md), the client treats it as REM (region Europe). Event types are mapped onto the same delivery column as PEC:

• SubmissionAcceptance → accepted by the QTSP;
• Delivery / LRE or AR24 avis de réception / De-Mail Zustellung / acuse de recibo → deposited;
• ContentConsignment / Retrieval / De-Mail Abholbestätigung → the recipient retrieved the content (closest European equivalent of “read”);
• rejection, virus, non-delivery, DeliveryExpiration → failed.

S/MIME (smime.p7s / smime.p7m) is shown as digitally signed; it is not PEC and not REM.

Delivery column after send

After SMTP send, Postclient stores the outbound Message-Id and, when you open Sent, reconciles gestore ricevute from Inbox and Ricevute. Matching uses, in order: daticert.xml <msgid>, X-Riferimento-Message-ID, In-Reply-To, PEC identificativo, then subject prefixes (ACCETTAZIONE:, CONSEGNA:, AVIS DE RECEPTION:, ACUSE DE RECIBO:, ZUSTELLBESTAETIGUNG:, ABHOLBESTAETIGUNG:, …).

Evidence	Mark	Meaning
PEC accettazione / presa-in-carico, ETSI SubmissionAcceptance	Accepted	The gestore took the message
PEC avvenuta-consegna, ETSI Delivery, LRE/AR24 avis, De-Mail Zustellung	Delivered	Deposited in the recipient certified mailbox — Italian PEC has no read receipt
ETSI ContentConsignment / Retrieval, De-Mail Abholbestätigung	Retrieved	Recipient picked up the content
non-accettazione, mancata-consegna, virus, ETSI rejection	Failed	Gestore reported non-acceptance or failed delivery

This client shows operator evidence. It does not issue a qualified ricevuta, PEC envelope, or timestamp.

Desktop notices fire for new PEC, ricevute, and REM (Windows toast, macOS notification, Linux notify-send).

Reading, folders, compose

• Folder tree follows the server (Inbox, Ricevute/Receipts, Drafts, Sent, Archive, Junk, Trash, plus custom folders). System folders cannot be deleted. You can create a folder, empty one (to Trash, or permanently in Trash), mark all read/unread, delete a custom folder, and drag messages onto a folder.
• List columns: unread, flag, attachments, delivery, type (PEC / RIC / REM / SIG), from, subject, date (local yyyy-MM-dd HH:mm), practice label.
• View: HTML (OS web engine), plain text, raw source, or FatturaPA. Layout: list above reading, or three columns (folders, list, reading).
• Group conversations indents replies in the folder list using Message-ID / In-Reply-To / References (depth up to 8). PEC ricevute that share the same original sit together. There is no separate conversation pane.
• Message actions: reply, reply all, forward, open in a new window, read/unread, flag, priority, delete.
• Compose is plain text. To, Cc, Bcc are address chips. Attachments are listed on the composer. Send uses the selected mailbox’s SMTP identity only.

HTML uses the OS engine: WebView2 on Windows (profile under the data folder), WebKitGTK on Linux, WKWebView on macOS. If the engine is missing, the text body is shown instead.

Linux packages for the HTML view:

sudo apt install libgtk-3-0 libwebkit2gtk-4.1-0 libsoup-3.0-0

Fedora: gtk3 webkit2gtk4.1 libsoup3.

Archive, search, labels

Get Messages indexes the whole IMAP folder into a local SQLite store (mail.db) plus .eml objects on disk. POP3 only fills Inbox. Indexing runs in the background; the status bar shows progress.

Search (current folder) covers subject, body, attachment text (PDF and text/XML/HTML/CSV/JSON), and practice labels. Labels exist only on this PC.

The archive is only on this PC. File → Open archive folder / Export archive copies mail.db and the .eml files. Paths:

OS	Config	Data
Windows	%AppData%\Postclient\	%LocalAppData%\Postclient\
Linux	~/.config/postclient/	~/.local/share/postclient/
macOS	~/Library/Application Support/Postclient/	same

Override with POSTCLIENT_CONFIG / POSTCLIENT_DATA_DIR. A portable Windows zip that contains settings.json with installType: portable keeps config next to the executable.

IMAP QUOTA from the gestore (when the server supports it) is shown in the status bar. That is the operator mailbox, not cloud storage from this application.

Import, export, print

Action	What you get
Import EML	Originals into the current folder
Import Thunderbird	Local mbox stores from the Thunderbird profile
Import Outlook PST/OST	Mail without installing Outlook
Print	Readable HTML of the (optionally unwrapped) message
Save PDF	Same content as a PDF
Save attachments ZIP	All attachments of the open message
Export selected EML (fascicolo)	The original .eml files — what a notaio or PA can keep as the message

Opened messages are also stored as .eml under the data folder. The .eml files are the originals; PDF/print are a reading copy.

Interface language

View → Language: English or Italiano. Folder names from the server (Posta in arrivo, Gesendet, Messages envoyés, Enviados, …) are mapped to Inbox/Sent/… in the UI language.

Downloads

When a GitHub Release exists: Windows portable zip and setup (postclient-{version}.exe, self-contained — no .NET SDK on the PC), Linux Flatpak, macOS DMG (osx-arm64 and osx-x64). macOS builds are unsigned: first launch is Open from the context menu. WinGet listing comes later from the same setup exe.

Linux (Flatpak)

GitHub releases include postclient-{version}.flatpak when the Windows release run finds WSL Debian + Flatpak builder.

flatpak install --user ./postclient-{version}.flatpak
flatpak run eu.postclient.desktop

Run from source

dotnet run --project src/MaksIT.PostClient.UI

From src/ so global.json applies:

cd src
dotnet build MaksIT.PostClient.slnx

Tests

utils\Invoke-TestEngine.bat

Coverage shields at the top of this file are maintained by the test engine (CoverageBadges).

Release

1. Update CHANGELOG.md and bump <Version> in src/Directory.Build.props.
2. Tag v{version} on main when a remote exists.
3. Run utils\Invoke-ReleasePackage.bat (self-contained Windows zip + setup exe, Linux Flatpak via WSL). Publishing the GitHub Release starts macOS release assets, which attaches unsigned osx-arm64 and osx-x64 DMGs.

License

Apache License 2.0. Copyright 2026 Maksym Sadovnychyy (MAKS-IT).