This is a sample LOG of an email with the described issue:
[2017.10.06] 11:25:36 [06914] Delivery started for angela@umfsrl.it at 11:25:36
[2017.10.06] 11:25:45 [06914] Skipping spam checks: No local recipients
[2017.10.06] 11:25:48 [06914] Sending remote mail for angela@umfsrl.it
[2017.10.06] 11:25:48 [06914] Spam check results: [_CUSTOMRULES: ], [_BAYESIANFILTERING: passed], [SURBL: passed], [URIBL: passed]
[2017.10.06] 11:25:48 [06914] Initiating connection to 213.205.33.63
[2017.10.06] 11:25:48 [06914] Connecting to 213.205.33.63:25 (Id: 1)
[2017.10.06] 11:25:48 [06914] Binding to local IP 192.168.1.161:0 (Id: 1)
[2017.10.06] 11:25:48 [06914] Connection to 213.205.33.63:25 from 192.168.1.161:64270 succeeded (Id: 1)
[2017.10.06] 11:26:02 [06914] RSP: 220 cmgw-3.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:26:02 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:26:02 [06914] RSP: 250-cmgw-3.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:26:02 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:26:02 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:26:02 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:26:02 [06914] RSP: 250 OK
[2017.10.06] 11:26:02 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:26:03 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:26:03 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:26:03 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:26:03 [06914] CMD: DATA
[2017.10.06] 11:26:03 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:29:03 [06914] The smtp session has timed out.
[2017.10.06] 11:29:03 [06914] Initiating connection to 213.205.33.64
[2017.10.06] 11:29:03 [06914] Connecting to 213.205.33.64:25 (Id: 2)
[2017.10.06] 11:29:03 [06914] Binding to local IP 192.168.1.161:0 (Id: 2)
[2017.10.06] 11:29:03 [06914] Connection to 213.205.33.64:25 from 192.168.1.161:64310 succeeded (Id: 2)
[2017.10.06] 11:29:17 [06914] RSP: 220 cmgw-2.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:29:17 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:29:17 [06914] RSP: 250-cmgw-2.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:29:17 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:29:17 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:29:17 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:29:17 [06914] RSP: 250 OK
[2017.10.06] 11:29:17 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:29:17 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:29:17 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:29:17 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:29:17 [06914] CMD: DATA
[2017.10.06] 11:29:17 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:32:17 [06914] The smtp session has timed out.
[2017.10.06] 11:32:17 [06914] Initiating connection to 213.205.33.61
[2017.10.06] 11:32:17 [06914] Connecting to 213.205.33.61:25 (Id: 3)
[2017.10.06] 11:32:17 [06914] Binding to local IP 192.168.1.161:0 (Id: 3)
[2017.10.06] 11:32:17 [06914] Connection to 213.205.33.61:25 from 192.168.1.161:64351 succeeded (Id: 3)
[2017.10.06] 11:32:31 [06914] RSP: 220 cmgw-2.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:32:31 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:32:31 [06914] RSP: 250-cmgw-2.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:32:31 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:32:31 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:32:31 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:32:31 [06914] RSP: 250 OK
[2017.10.06] 11:32:31 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:32:31 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:32:31 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:32:31 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:32:31 [06914] CMD: DATA
[2017.10.06] 11:32:31 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:35:31 [06914] The smtp session has timed out.
[2017.10.06] 11:35:31 [06914] Initiating connection to 213.205.33.62
[2017.10.06] 11:35:31 [06914] Connecting to 213.205.33.62:25 (Id: 4)
[2017.10.06] 11:35:31 [06914] Binding to local IP 192.168.1.161:0 (Id: 4)
[2017.10.06] 11:35:31 [06914] Connection to 213.205.33.62:25 from 192.168.1.161:64412 succeeded (Id: 4)
[2017.10.06] 11:35:45 [06914] RSP: 220 cmgw-3.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:35:45 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:35:46 [06914] RSP: 250-cmgw-3.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:35:46 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:35:46 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:35:46 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:35:46 [06914] RSP: 250 OK
[2017.10.06] 11:35:46 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:35:46 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:35:46 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:35:46 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:35:46 [06914] CMD: DATA
[2017.10.06] 11:35:46 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:38:46 [06914] The smtp session has timed out.
[2017.10.06] 11:38:46 [06914] Initiating connection to 213.205.33.62
[2017.10.06] 11:38:46 [06914] Connecting to 213.205.33.62:25 (Id: 5)
[2017.10.06] 11:38:46 [06914] Binding to local IP 192.168.1.161:0 (Id: 5)
[2017.10.06] 11:38:46 [06914] Connection to 213.205.33.62:25 from 192.168.1.161:64451 succeeded (Id: 5)
[2017.10.06] 11:39:00 [06914] RSP: 220 cmgw-3.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:39:00 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:39:00 [06914] RSP: 250-cmgw-3.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:39:00 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:39:00 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:39:00 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:39:00 [06914] RSP: 250 OK
[2017.10.06] 11:39:00 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:39:00 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:39:00 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:39:00 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:39:00 [06914] CMD: DATA
[2017.10.06] 11:39:00 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:42:00 [06914] The smtp session has timed out.
[2017.10.06] 11:42:00 [06914] Initiating connection to 213.205.33.63
[2017.10.06] 11:42:00 [06914] Connecting to 213.205.33.63:25 (Id: 6)
[2017.10.06] 11:42:00 [06914] Binding to local IP 192.168.1.161:0 (Id: 6)
[2017.10.06] 11:42:00 [06914] Connection to 213.205.33.63:25 from 192.168.1.161:64481 succeeded (Id: 6)
[2017.10.06] 11:42:14 [06914] RSP: 220 cmgw-4.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:42:14 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:42:14 [06914] RSP: 250-cmgw-4.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:42:14 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:42:14 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:42:14 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:42:14 [06914] RSP: 250 OK
[2017.10.06] 11:42:14 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:42:14 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:42:14 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:42:15 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:42:15 [06914] CMD: DATA
[2017.10.06] 11:42:15 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:45:15 [06914] The smtp session has timed out.
[2017.10.06] 11:45:15 [06914] Initiating connection to 213.205.33.64
[2017.10.06] 11:45:15 [06914] Connecting to 213.205.33.64:25 (Id: 7)
[2017.10.06] 11:45:15 [06914] Binding to local IP 192.168.1.161:0 (Id: 7)
[2017.10.06] 11:45:15 [06914] Connection to 213.205.33.64:25 from 192.168.1.161:64512 succeeded (Id: 7)
[2017.10.06] 11:45:29 [06914] RSP: 220 cmgw-2.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:45:29 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:45:29 [06914] RSP: 250-cmgw-2.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:45:29 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:45:29 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:45:29 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:45:29 [06914] RSP: 250 OK
[2017.10.06] 11:45:29 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:45:29 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:45:29 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:45:29 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:45:29 [06914] CMD: DATA
[2017.10.06] 11:45:29 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:48:29 [06914] The smtp session has timed out.
[2017.10.06] 11:48:29 [06914] Initiating connection to 213.205.33.61
[2017.10.06] 11:48:29 [06914] Connecting to 213.205.33.61:25 (Id: 8)
[2017.10.06] 11:48:29 [06914] Binding to local IP 192.168.1.161:0 (Id: 8)
[2017.10.06] 11:48:29 [06914] Connection to 213.205.33.61:25 from 192.168.1.161:64546 succeeded (Id: 8)
[2017.10.06] 11:48:43 [06914] RSP: 220 cmgw-4.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:48:43 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:48:43 [06914] RSP: 250-cmgw-4.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:48:43 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:48:43 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:48:43 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:48:43 [06914] RSP: 250 OK
[2017.10.06] 11:48:43 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:48:43 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:48:43 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:48:43 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:48:43 [06914] CMD: DATA
[2017.10.06] 11:48:43 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:51:43 [06914] The smtp session has timed out.
[2017.10.06] 11:51:43 [06914] Initiating connection to 213.205.33.62
[2017.10.06] 11:51:43 [06914] Connecting to 213.205.33.62:25 (Id: 9)
[2017.10.06] 11:51:43 [06914] Binding to local IP 192.168.1.161:0 (Id: 9)
[2017.10.06] 11:51:43 [06914] Connection to 213.205.33.62:25 from 192.168.1.161:64566 succeeded (Id: 9)
[2017.10.06] 11:51:57 [06914] RSP: 220 cmgw-4.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:51:57 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:51:58 [06914] RSP: 250-cmgw-4.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:51:58 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:51:58 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:51:58 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:51:58 [06914] RSP: 250 OK
[2017.10.06] 11:51:58 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:51:58 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:51:58 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:51:58 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:51:58 [06914] CMD: DATA
[2017.10.06] 11:51:58 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:54:58 [06914] The smtp session has timed out.
[2017.10.06] 11:54:58 [06914] Initiating connection to 213.205.33.61
[2017.10.06] 11:54:58 [06914] Connecting to 213.205.33.61:25 (Id: 10)
[2017.10.06] 11:54:58 [06914] Binding to local IP 192.168.1.161:0 (Id: 10)
[2017.10.06] 11:54:58 [06914] Connection to 213.205.33.61:25 from 192.168.1.161:64594 succeeded (Id: 10)
[2017.10.06] 11:55:12 [06914] RSP: 220 cmgw-1.mail.tiscali.it ESMTP service ready
[2017.10.06] 11:55:12 [06914] CMD: EHLO mail3.sersis.com
[2017.10.06] 11:55:12 [06914] RSP: 250-cmgw-1.mail.tiscali.it hello [151.80.62.161], pleased to meet you
[2017.10.06] 11:55:12 [06914] RSP: 250-SIZE 104857600
[2017.10.06] 11:55:12 [06914] RSP: 250-ENHANCEDSTATUSCODES
[2017.10.06] 11:55:12 [06914] RSP: 250-8BITMIME
[2017.10.06] 11:55:12 [06914] RSP: 250 OK
[2017.10.06] 11:55:12 [06914] CMD: MAIL FROM:<angela@umfsrl.it> SIZE=26037
[2017.10.06] 11:55:12 [06914] RSP: 250 2.1.0 <angela@umfsrl.it> sender ok
[2017.10.06] 11:55:12 [06914] CMD: RCPT TO:<mecsav@tiscali.it>
[2017.10.06] 11:55:12 [06914] RSP: 250 2.1.5 <mecsav@tiscali.it> recipient ok
[2017.10.06] 11:55:12 [06914] CMD: DATA
[2017.10.06] 11:55:12 [06914] RSP: 354 enter mail, end with "." on a line by itself
[2017.10.06] 11:55:47 [06914] RSP: 250 2.0.0 J9vL1w01g3Uk8nK019vLgB mail accepted for delivery
[2017.10.06] 11:55:47 [06914] CMD: QUIT
[2017.10.06] 11:55:47 [06914] RSP: 221 2.0.0 cmgw-1.mail.tiscali.it closing connection
[2017.10.06] 11:55:47 [06914] Delivery for angela@umfsrl.it to mecsav@tiscali.it has completed (Delivered)
[2017.10.06] 11:55:49 [06914] Delivery finished for angela@umfsrl.it at 11:55:49 [id:x86706914]