Hello there.bile. We have read your message. We try to help you. What antivirus do you guys have? Try to turn of the hardcore antivirus. And check your Smtp settings for that system. Mail domain settings. Send me the rapport of this link below. https://www.checktls.com/TestReceiver (Scannedvirustotal) Greetings Thunderbird volunteer.

antivirus is windows 10 defender, disabled for test SMTP Settings appear correct email test results: CheckTLS Confidence Factor for "halback@gru.net": 65 (114 max) MX Server Pref Answer Connect HELO TLS Cert Secure From MTASTS DANE Score mx3.smtp.gru.net [209.251.130.31:25] 0 OK (35ms) OK (123ms) OK (37ms) OK (34ms) FAIL OK (392ms) OK (35ms) not tested not tested 64.69 mx4.smtp.gru.net [209.251.130.41:25] 0 OK (34ms) OK (120ms) OK (33ms) OK (34ms) FAIL OK (357ms) OK (35ms) not tested not tested 64.69 mx1.smtp.gru.net [209.251.130.11:25] 5 OK (33ms) OK (117ms) OK (33ms) OK (33ms) FAIL OK (343ms) OK (38ms) not tested not tested 64.69 mx2.smtp.gru.net [209.251.130.21:25] 5 OK (34ms) OK (122ms) OK (34ms) OK (34ms) FAIL OK (359ms) OK (38ms) not tested not tested 64.69 Average 100% 100% 100% 100% 0% 100% 100% 65 Scan down DETAIL output below for info on errors and warnings. Checking halback@gru.net from www12-azure.checktls.com: seconds lookup result [000.000]      DNS LOOKUPS [000.001]      SEARCHLIST 104.131.108.216,134.209.169.224,1.1.1.1,8.8.8.8,67.207.67.3 [000.048]      MX (0) mx3.smtp.gru.net [000.048]      MX (0) mx4.smtp.gru.net [000.048]      MX (5) mx1.smtp.gru.net [000.048]      MX (5) mx2.smtp.gru.net [000.090]      MX:A-->mx3.smtp.gru.net 209.251.130.31 [000.130]      MX:A-->mx4.smtp.gru.net 209.251.130.41 [000.172]      MX:A-->mx1.smtp.gru.net 209.251.130.11 [000.213]      MX:A-->mx2.smtp.gru.net 209.251.130.21 seconds test stage and result [000.000] Trying TLS on mx3.smtp.gru.net[209.251.130.31:25] (0) [000.035] Server answered [000.158] <‑‑ 220 gc3.gru.net ESMTP service ready [000.158] We are allowed to connect [000.158] ‑‑> EHLO www12-azure.checktls.com [000.195] <‑‑ 250-gc3.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-STARTTLS 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.195] We can use this server [000.195] TLS is an option on this server [000.195] ‑‑> STARTTLS [000.229] <‑‑ 220 2.0.0 Ready to start TLS [000.229] STARTTLS command works on this server [000.350] Connection converted to SSL SSLVersion in use: TLSv1 SSL Version is insecure/deprecated (See NIST SP 800-52 Rev. 2) Cipher in use: DHE-RSA-AES256-SHA Perfect Forward Secrecy: yes Certificate #1 of 1 (sent by MX): Cert VALIDATION ERROR(S): unable to get local issuer certificate This may help: What Is An Intermediate Certificate So email is encrypted but the recipient domain is not verified Cert Hostname DOES NOT VERIFY (mx3.smtp.gru.net != *.gru.net | DNS:*.gru.net | DNS:vpn.gru.net | DNS:gru.net) (see RFC-2818 section 3.1 paragraph 4 for info on wildcard ("*") matching) So email is encrypted but the host is not verified Not Valid Before: Apr 8 00:00:00 2022 GMT Not Valid After: May 9 23:59:59 2023 GMT subject= /C=US/ST=Florida/L=GAINESVILLE/O=GRUCom/CN=*.gru.net issuer= /C=US/O=DigiCert Inc/CN=DigiCert TLS RSA SHA256 2020 CA1 [000.356] ~~> EHLO www12-azure.checktls.com [000.392] <~~ 250-gc3.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.392] TLS successfully started on this server [000.392] ~~> MAIL FROM:<test@checktls.com> [000.427] <~~ 250 2.1.0 Ok [000.427] Sender is OK [000.427] ~~> QUIT [000.462] <~~ 221 2.0.0 Bye seconds test stage and result [000.000] Trying TLS on mx4.smtp.gru.net[209.251.130.41:25] (0) [000.034] Server answered [000.154] <‑‑ 220 gc4.gru.net ESMTP service ready [000.154] We are allowed to connect [000.154] ‑‑> EHLO www12-azure.checktls.com [000.187] <‑‑ 250-gc4.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-STARTTLS 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.187] We can use this server [000.188] TLS is an option on this server [000.188] ‑‑> STARTTLS [000.221] <‑‑ 220 2.0.0 Ready to start TLS [000.221] STARTTLS command works on this server [000.318] Connection converted to SSL SSLVersion in use: TLSv1 SSL Version is insecure/deprecated (See NIST SP 800-52 Rev. 2) Cipher in use: DHE-RSA-AES256-SHA Perfect Forward Secrecy: yes Certificate #1 of 1 (sent by MX): Cert VALIDATION ERROR(S): unable to get local issuer certificate This may help: What Is An Intermediate Certificate So email is encrypted but the recipient domain is not verified Cert Hostname DOES NOT VERIFY (mx4.smtp.gru.net != *.gru.net | DNS:*.gru.net | DNS:vpn.gru.net | DNS:gru.net) (see RFC-2818 section 3.1 paragraph 4 for info on wildcard ("*") matching) So email is encrypted but the host is not verified Not Valid Before: Apr 8 00:00:00 2022 GMT Not Valid After: May 9 23:59:59 2023 GMT subject= /C=US/ST=Florida/L=GAINESVILLE/O=GRUCom/CN=*.gru.net issuer= /C=US/O=DigiCert Inc/CN=DigiCert TLS RSA SHA256 2020 CA1 [000.322] ~~> EHLO www12-azure.checktls.com [000.357] <~~ 250-gc4.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.357] TLS successfully started on this server [000.357] ~~> MAIL FROM:<test@checktls.com> [000.391] <~~ 250 2.1.0 Ok [000.391] Sender is OK [000.391] ~~> QUIT [000.425] <~~ 221 2.0.0 Bye seconds test stage and result [000.000] Trying TLS on mx1.smtp.gru.net[209.251.130.11:25] (5) [000.033] Server answered [000.150] <‑‑ 220 gc1.gru.net ESMTP service ready [000.150] We are allowed to connect [000.150] ‑‑> EHLO www12-azure.checktls.com [000.182] <‑‑ 250-gc1.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-STARTTLS 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.183] We can use this server [000.183] TLS is an option on this server [000.183] ‑‑> STARTTLS [000.215] <‑‑ 220 2.0.0 Ready to start TLS [000.215] STARTTLS command works on this server [000.307] Connection converted to SSL SSLVersion in use: TLSv1 SSL Version is insecure/deprecated (See NIST SP 800-52 Rev. 2) Cipher in use: DHE-RSA-AES256-SHA Perfect Forward Secrecy: yes Certificate #1 of 1 (sent by MX): Cert VALIDATION ERROR(S): unable to get local issuer certificate This may help: What Is An Intermediate Certificate So email is encrypted but the recipient domain is not verified Cert Hostname DOES NOT VERIFY (mx1.smtp.gru.net != *.gru.net | DNS:*.gru.net | DNS:vpn.gru.net | DNS:gru.net) (see RFC-2818 section 3.1 paragraph 4 for info on wildcard ("*") matching) So email is encrypted but the host is not verified Not Valid Before: Apr 8 00:00:00 2022 GMT Not Valid After: May 9 23:59:59 2023 GMT subject= /C=US/ST=Florida/L=GAINESVILLE/O=GRUCom/CN=*.gru.net issuer= /C=US/O=DigiCert Inc/CN=DigiCert TLS RSA SHA256 2020 CA1 [000.311] ~~> EHLO www12-azure.checktls.com [000.343] <~~ 250-gc1.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.343] TLS successfully started on this server [000.343] ~~> MAIL FROM:<test@checktls.com> [000.381] <~~ 250 2.1.0 Ok [000.381] Sender is OK [000.381] ~~> QUIT [000.414] <~~ 221 2.0.0 Bye seconds test stage and result [000.000] Trying TLS on mx2.smtp.gru.net[209.251.130.21:25] (5) [000.034] Server answered [000.156] <‑‑ 220 gc2.gru.net ESMTP service ready [000.156] We are allowed to connect [000.156] ‑‑> EHLO www12-azure.checktls.com [000.190] <‑‑ 250-gc2.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-STARTTLS 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.190] We can use this server [000.190] TLS is an option on this server [000.190] ‑‑> STARTTLS [000.224] <‑‑ 220 2.0.0 Ready to start TLS [000.224] STARTTLS command works on this server [000.320] Connection converted to SSL SSLVersion in use: TLSv1 SSL Version is insecure/deprecated (See NIST SP 800-52 Rev. 2) Cipher in use: DHE-RSA-AES256-SHA Perfect Forward Secrecy: yes Certificate #1 of 1 (sent by MX): Cert VALIDATION ERROR(S): unable to get local issuer certificate This may help: What Is An Intermediate Certificate So email is encrypted but the recipient domain is not verified Cert Hostname DOES NOT VERIFY (mx2.smtp.gru.net != *.gru.net | DNS:*.gru.net | DNS:vpn.gru.net | DNS:gru.net) (see RFC-2818 section 3.1 paragraph 4 for info on wildcard ("*") matching) So email is encrypted but the host is not verified Not Valid Before: Apr 8 00:00:00 2022 GMT Not Valid After: May 9 23:59:59 2023 GMT subject= /C=US/ST=Florida/L=GAINESVILLE/O=GRUCom/CN=*.gru.net issuer= /C=US/O=DigiCert Inc/CN=DigiCert TLS RSA SHA256 2020 CA1 [000.325] ~~> EHLO www12-azure.checktls.com [000.359] <~~ 250-gc2.gru.net 250-PIPELINING 250-SIZE 15360000 250-ETRN 250-ENHANCEDSTATUSCODES 250-8BITMIME 250 DSN [000.359] TLS successfully started on this server [000.360] ~~> MAIL FROM:<test@checktls.com> [000.397] <~~ 250 2.1.0 Ok [000.397] Sender is OK [000.397] ~~> QUIT [000.431] <~~ 221 2.0.0 Bye