diff --git a/app/api/migrations/migrations/36-populate-mimetype-on-attachments/index.js b/app/api/migrations/migrations/36-populate-mimetype-on-attachments/index.js
new file mode 100644
index 0000000000..db2e54dd8a
--- /dev/null
+++ b/app/api/migrations/migrations/36-populate-mimetype-on-attachments/index.js
@@ -0,0 +1,38 @@
+import request from 'shared/JSONRequest';
+import { attachmentsPath } from 'api/files/filesystem';
+import mime from 'mime-types';
+
+export default {
+  delta: 36,
+
+  name: 'populate-mimetype-to-attachment',
+
+  description: 'Populates mimetype of an attachment from a url',
+
+  async up(db) {
+    process.stdout.write(`${this.name}...\r\n`);
+    const cursor = await db.collection('files').find({});
+
+    // eslint-disable-next-line no-await-in-loop
+    while (await cursor.hasNext()) {
+      // eslint-disable-next-line no-await-in-loop
+      const file = await cursor.next();
+      if (file.url && !file.mimetype) {
+        // eslint-disable-next-line no-await-in-loop
+        const response = await request.head(file.url);
+        const mimetype = response.headers.get('content-type') || undefined;
+        // eslint-disable-next-line no-await-in-loop
+        await this.updateFile(db, file, mimetype);
+      } else if (file.filename && file.type === 'attachment' && !file.mimetype) {
+        const mimetype = mime.lookup(attachmentsPath(file.filename)) || undefined;
+        // eslint-disable-next-line no-await-in-loop
+        await this.updateFile(db, file, mimetype);
+      }
+    }
+  },
+  async updateFile(db, file, mimetype) {
+    if (mimetype) {
+      await db.collection('files').updateOne({ _id: file._id }, { $set: { mimetype } });
+    }
+  },
+};
diff --git a/app/api/migrations/migrations/36-populate-mimetype-on-attachments/specs/36-populate-mimetype-on-attachments.spec.js b/app/api/migrations/migrations/36-populate-mimetype-on-attachments/specs/36-populate-mimetype-on-attachments.spec.js
new file mode 100644
index 0000000000..a9c9cb97ca
--- /dev/null
+++ b/app/api/migrations/migrations/36-populate-mimetype-on-attachments/specs/36-populate-mimetype-on-attachments.spec.js
@@ -0,0 +1,165 @@
+import testingDB from 'api/utils/testing_db';
+import request from 'shared/JSONRequest';
+import * as attachmentMethods from 'api/files/filesystem';
+import mime from 'mime-types';
+import migration from '../index.js';
+
+describe('migration populate-mimetype-on-attachments', () => {
+  let headRequestMock;
+  let attachmentPathMock;
+  let mimeMock;
+
+  beforeEach(async () => {
+    spyOn(process.stdout, 'write');
+    headRequestMock = spyOn(request, 'head');
+    attachmentPathMock = spyOn(attachmentMethods, 'attachmentsPath');
+    mimeMock = spyOn(mime, 'lookup');
+  });
+
+  afterAll(async () => {
+    headRequestMock.mockRestore();
+    attachmentPathMock.mockRestore();
+    mimeMock.mockRestore();
+    await testingDB.disconnect();
+  });
+
+  it('should have a delta number', () => {
+    expect(migration.delta).toBe(36);
+  });
+
+  it('should populate mimetype with Content-Type', async () => {
+    const fixtures = {
+      files: [{ url: 'some/file/path.jpg' }, { url: 'some/other/path.jpg' }],
+    };
+    await testingDB.clearAllAndLoad(fixtures);
+    const headers = {
+      get: jest
+        .fn()
+        .mockReturnValueOnce('application/pdf')
+        .mockReturnValueOnce('mimetype2'),
+    };
+    headRequestMock.and.returnValue(
+      Promise.resolve({
+        headers,
+      })
+    );
+    await migration.up(testingDB.mongodb);
+    expect(request.head).toHaveBeenCalledWith(fixtures.files[0].url);
+    expect(request.head).toHaveBeenCalledWith(fixtures.files[1].url);
+    expect(headers.get).toHaveBeenCalledWith('content-type');
+
+    const files = await testingDB.mongodb
+      .collection('files')
+      .find({})
+      .toArray();
+
+    expect(files[0].mimetype).toEqual('application/pdf');
+    expect(files[1].mimetype).toEqual('mimetype2');
+  });
+
+  it('should not change the value of mimetype if it already exists in external attachments', async () => {
+    const fixturesWithMimetype = {
+      files: [
+        {
+          url: 'some/url/item.jpg',
+          mimetype: 'application/pdf',
+        },
+      ],
+    };
+    await testingDB.clearAllAndLoad(fixturesWithMimetype);
+
+    const file = await testingDB.mongodb.collection('files').findOne({});
+
+    expect(file.mimetype).toEqual(fixturesWithMimetype.files[0].mimetype);
+  });
+
+  it('should not change if value of mimetype already exists in internal attachments', async () => {
+    const fixturesWithFilenames = {
+      files: [
+        {
+          filename: 'somename.pdf',
+          mimetype: 'application/pdf',
+          type: 'attachment',
+        },
+      ],
+    };
+    await testingDB.clearAllAndLoad(fixturesWithFilenames);
+    attachmentPathMock.and.returnValue('/some/path/to/file.pdf');
+    mimeMock.and.returnValue('application/pdf');
+    await migration.up(testingDB.mongodb);
+
+    const file = await testingDB.mongodb.collection('files').findOne({});
+    expect(file.mimetype).toEqual(fixturesWithFilenames.files[0].mimetype);
+  });
+
+  it('should update mimetype if filename exists in internal attachments', async () => {
+    const fixturesWithFilenames = {
+      files: [
+        {
+          filename: 'somename.pdf',
+          type: 'attachment',
+        },
+      ],
+    };
+    await testingDB.clearAllAndLoad(fixturesWithFilenames);
+    mimeMock.and.returnValue('application/pdf');
+    attachmentPathMock.and.returnValue('/some/path/to/file.pdf');
+    await migration.up(testingDB.mongodb);
+
+    const file = await testingDB.mongodb.collection('files').findOne({});
+    expect(file.mimetype).toEqual('application/pdf');
+    expect(attachmentMethods.attachmentsPath).toHaveBeenCalledWith(
+      fixturesWithFilenames.files[0].filename
+    );
+    expect(mime.lookup).toHaveBeenCalledWith('/some/path/to/file.pdf');
+  });
+  it('should not update mimetype if type is not attachment in internal attachments', async () => {
+    const fixturesWithFilenames = {
+      files: [
+        {
+          filename: 'somename.pdf',
+          type: 'document',
+        },
+      ],
+    };
+    await testingDB.clearAllAndLoad(fixturesWithFilenames);
+    mimeMock.and.returnValue('application/pdf');
+    attachmentPathMock.and.returnValue('/some/path/to/file.pdf');
+    await migration.up(testingDB.mongodb);
+
+    expect(attachmentMethods.attachmentsPath).not.toHaveBeenCalledWith(
+      fixturesWithFilenames.files[0].filename
+    );
+    expect(mime.lookup).not.toHaveBeenCalledWith('/some/path/to/file.pdf');
+  });
+  it('should not use local attachment if url field is present', async () => {
+    const mixedFixtures = {
+      files: [
+        {
+          filename: 'somename.pdf',
+          type: 'attachment',
+          url: '/some/url/to/file.something',
+        },
+      ],
+    };
+    await testingDB.clearAllAndLoad(mixedFixtures);
+    const headers = {
+      get: jest
+        .fn()
+        .mockReturnValueOnce('application/pdf')
+        .mockReturnValueOnce('mimetype2'),
+    };
+    headRequestMock.and.returnValue(
+      Promise.resolve({
+        headers,
+      })
+    );
+    mimeMock.and.returnValue('application/pdf');
+    attachmentPathMock.and.returnValue('/some/path/to/file.pdf');
+    await migration.up(testingDB.mongodb);
+
+    expect(attachmentMethods.attachmentsPath).not.toHaveBeenCalled();
+    expect(mime.lookup).not.toHaveBeenCalled();
+    expect(request.head).toHaveBeenCalledWith(mixedFixtures.files[0].url);
+  });
+});
diff --git a/package.json b/package.json
index 2136c743f7..dfae563e7f 100644
--- a/package.json
+++ b/package.json
@@ -112,6 +112,7 @@
     "mark.js": "^8.11.1",
     "markdown-it": "11.0.0",
     "markdown-it-container": "3.0.0",
+    "mime-types": "^2.1.29",
     "moment": "2.27.0",
     "moment-timezone": "0.5.31",
     "mongodb": "^3.6.2",
diff --git a/yarn.lock b/yarn.lock
index 20b664de43..e466648f41 100644
--- a/yarn.lock
+++ b/yarn.lock
@@ -9428,6 +9428,11 @@ mime-db@1.45.0:
   resolved "https://registry.yarnpkg.com/mime-db/-/mime-db-1.45.0.tgz#cceeda21ccd7c3a745eba2decd55d4b73e7879ea"
   integrity sha512-CkqLUxUk15hofLoLyljJSrukZi8mAtgd+yE5uO4tqRZsdsAJKv0O+rFMhVDRJgozy+yG6md5KwuXhD4ocIoP+w==
 
+mime-db@1.46.0:
+  version "1.46.0"
+  resolved "https://registry.yarnpkg.com/mime-db/-/mime-db-1.46.0.tgz#6267748a7f799594de3cbc8cde91def349661cee"
+  integrity sha512-svXaP8UQRZ5K7or+ZmfNhg2xX3yKDMUzqadsSqi4NCH/KomcH75MAMYAGVlvXn4+b/xOPhS3I2uHKRUzvjY7BQ==
+
 mime-db@~1.33.0:
   version "1.33.0"
   resolved "https://registry.yarnpkg.com/mime-db/-/mime-db-1.33.0.tgz#a3492050a5cb9b63450541e39d9788d2272783db"
@@ -9439,6 +9444,13 @@ mime-types@^2.1.12, mime-types@~2.1.19:
   dependencies:
     mime-db "1.45.0"
 
+mime-types@^2.1.29:
+  version "2.1.29"
+  resolved "https://registry.yarnpkg.com/mime-types/-/mime-types-2.1.29.tgz#1d4ab77da64b91f5f72489df29236563754bb1b2"
+  integrity sha512-Y/jMt/S5sR9OaqteJtslsFZKWOIIqMACsJSiHghlCAyhf7jfVYjKBmLiX8OgpWeW+fjJ2b+Az69aPFPkUOY6xQ==
+  dependencies:
+    mime-db "1.46.0"
+
 mime-types@~2.1.17, mime-types@~2.1.18:
   version "2.1.18"
   resolved "https://registry.yarnpkg.com/mime-types/-/mime-types-2.1.18.tgz#6f323f60a83d11146f831ff11fd66e2fe5503bb8"