Portal reset password fails with the Unable to send email. Contact the site administrator if the problem persists error message in UI

From the logs of portal *www* pod's admin container :
[     queue stderr] id id:id:id timestamp snapshot: WATCHDOG: [ERROR] [mail] Error sending email (from user1@ibm.com to user1@ibm.com with reply-to null@example.com). | user: anonymous | uri: http://portal_url/ | referer: ^M
[     queue stderr] id id:id:id timestamp snapshot:  [error]  Error sending email (from user1@ibm.com to user1@ibm.com with reply-to null@example.com).
[     queue stderr] id id:id:id timestamp snapshot: WATCHDOG: [INFO] [ibm_apim] Sent welcome mail to user1@ibm.com | user: anonymous | uri: http://portal_url/ | referer: ^M
[     queue stderr] id id:id:id timestamp snapshot:  [error]  Message: Unable to send email. Contact the site administrator if the problem persists.

From the logs of management *apim* pod:
timestamp apim:error [id] Error sending email: connect ECONNREFUSED ::1:587, stack: Error: connect ECONNREFUSED ::1:587
    at __node_internal_captureLargerStackTrace (node:internal/errors:496:5)
    at __node_internal_exceptionWithHostPort (node:internal/errors:671:12)
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1555:16)
timestamp apim:error [id] Error connecting to mail server localhost:587: connect ECONNREFUSED ::1:587, stack: Error: connect ECONNREFUSED ::1:587
    at __node_internal_captureLargerStackTrace (node:internal/errors:496:5)
    at __node_internal_exceptionWithHostPort (node:internal/errors:671:12)
    at TCPConnectWrap.afterConnect [as oncomplete] (node:net:1555:16)
2024-04-14T08:06:38.769Z bhendi:error [id] Error in POST post:/api/catalogs/:org/:catalog/send-email (catalog.js:sendEmail)
  - status : 400
  - message: Error sending mail message using mail server named dummy-mail-server (Dummy Mail Server) with host localhost and port 587 (connect ECONNREFUSED ::1:587).
  - stack  : Error: Error sending mail message using mail server named dummy-mail-server (Dummy Mail Server) with host localhost and port 587 (connect ECONNREFUSED ::1:587).
    at error (/app/node_modules/@apic/apic-util/src/util.js:841:11)
    at sendMessageUtility (/lib/emailNotificationType.js:208:15)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at Catalog.sendEmail (/routes/catalog.js:1385:9)
    at async dispatch (/app/node_modules/bhendi/mw/dispatcher.js:411:20)
    at async dispatcher (/app/node_modules/bhendi/mw/dispatcher.js:332:5)
  - errors : undefined: {"status":400,"message":["Error sending mail message using mail server named dummy-mail-server (Dummy Mail Server) with host localhost and port 587 (connect ECONNREFUSED ::1:587)."]}
timestamp bhendi:server [id]   - Serializing as application/json
timestamp audit [id] Stack trace for response error: Error: Error sending mail message using mail server named dummy-mail-server (Dummy Mail Server) with host localhost and port 587 (connect ECONNREFUSED ::1:587).
    at error (/app/node_modules/bhendi/lib/bhendiUtil.js:61:11)
    at dispatch (/app/node_modules/bhendi/mw/dispatcher.js:528:21)
    at process.processTicksAndRejections (node:internal/process/task_queues:95:5)
    at async dispatcher (/app/node_modules/bhendi/mw/dispatcher.js:332:5)
timestamp audit [id] END:   <<<<<<<< FAILURE: [400] response (POST /api/catalogs/id/id/send-email) (took 87ms)
[id] {
    "status": 400,
    "message": [
        "Error sending mail message using mail server named dummy-mail-server (Dummy Mail Server) with host localhost and port 587 (connect ECONNREFUSED ::1:587)."
    ]
}