In short: Mercurio is the official platform to submit immigration authorisation applications (initial and renewals) online, using a digital certificate or DNIe; at the end you get a resguardo (receipt), which is the valid proof of submission.
In person or by representative? Filing is fully online: you do it with a certificate/DNIe, or through a representative (gestor administrativo, graduado social). Note: after approval, the TIE and fingerprints are done in person.
The channel is the electronic headquarters: sede.administracionespublicas.gob.es → Mercurio. Authentication uses Cl@ve plus a personal certificate installed in your browser (or DNIe); you can act yourself or through a representative (gestor administrativo, graduado social). You need the AutoFirma program to sign. To obtain the certificate or Cl@ve, see Cl@ve and electronic certificate. Each form (EX-xx) is chosen inside the app; the official forms are here. Important: Mercurio covers the filing; if your initial authorisation is not implemented in Mercurio, it is filed via the Electronic Register or in person. After approval, the TIE and fingerprints are done in person.
Steps:
- Get a digital certificate or DNIe and install AutoFirma.
- Go to Mercurio (sede → Procedimientos → Extranjería), authenticate with Cl@ve and pick your province.
- "Create initial application" and select the relevant form (EX-xx).
- Fill in the data and attach the documents (PDF, max 6 MB per file).
- Sign with AutoFirma and register → "Download resguardo" (valid receipt).
- Check the status at infoext2 with your NIE or file number.
Official source: Mercurio — Telematic immigration authorisation applications. Informational only; check the official source and a professional for your specific case.