Hi, Some thoughts. 1. Rather than MTU you might be better off changing the MSS down a bit leaving the MTU where it should be. The following is set for the common 1452 (for 1492 MTU), you might want to try something less. eg. 1440, 1400 Note: need to change both the 1452 and 1453 items. (There is also clamp to pmtu option available, sorry, no idea how that works) set up mss for pppoe connection(s) /ip firewall mangle add action=change-mss chain=forward new-mss=1452 out-interface=pppoe-out1 \ passthrough=yes protocol=tcp tcp-flags=syn tcp-mss=1453-65535 add action=change-mss chain=forward in-interface=pppoe-out1 new-mss=1452 \ passthrough=yes protocol=tcp tcp-flags=syn tcp-mss=1453-65535 2. When the send/draft is failing (and when it's working so you have a baseline) Look at task manager performance screen. (Is network send close to maxed out? 0.4M) Check outbound interface throughput on Mikrotik, is it at maximum? Does the inbound rate seem reasonable. Check the ip firewall connections screen, is it just the IMAP port from the Laptop using internet, or is something else going on? 3. Do you have queues on the Mikrotik, Are they dropping lots, none? If present, try with them turned off If not present, add an outbound queue onto the pppoe interface. (Maybe pcq upload default, max limit 0.4M or there abouts) If adding a queue helps, Ros V7 has newer queue types: cake and fq_codel that are apparently very good. When faulty, perhaps the outbound limit is < 0.4M, ask the modem what it is. 4. Install wireshark and look at what is happening. (sort of, given it's all likely inside TLS) it still might give you some hints. (lots of duplicated packets, etc) Regards Roger From: Karl Auer <kauer@nullarbor.com.au> To: MikroTik Public <public@talk.mikrotik.com.au> Date sent: Fri, 08 Apr 2022 16:14:05 +1000 Organization: Nullarbor Consulting pty Ltd Subject: [MT-AU Public] Odd IMAP failures, seems to be network Send reply to: kauer@nullarbor.com.au, MikroTik Australia Public List <public@talk.mikrotik.com.au> [ Double-click this line for list subscription options ] I run a Mikrotik router as my home router, have done for years. I personally have never had an issue with it. The current one is an hAP ac^3 running 6.47.10 with plenty of free RAM and disk space and virtually zero CPU usage. However one of my "users", running Thunderbird on Windows, has an ongoing problem using IMAP. When she sends an email, the email is not saved to the (IMAP) "Sent" folder. If she saves a draft, it fails to save to the (IMAP) "Drafts" folder. In both cases the failure comes after a long wait, indicating IMHO a network problem. This does not happen all the time, but often enough (well more than half the time) to be extremely frustrating. We can discern no commonality between the affected messages - large, small, addressees, attachments etc. Sometimes if she disconnects from the network and then reconnects, the message will work the second time around, but IMHO this is just blind luck. The thing is, this does NOT happen when she is using the same computer outside our home - on a public network, her phone's hotspot or whatever. Only at home. I have excluded wifi as the problem; she gets the same issue on a wired connection. I have set up my own IMAP connection (though not as yet with Thunderbird) and cannot replicate the problem. She and I use the same local network, the same email provider and the same connectivity provider (ADSL from iiNet). The link is slow (about 14/0.4), but has been dependable and as I say, I do not have any problem other than with speed. This has been going on for probably about two years now, getting steadily worse, to the point where she now leaves the house to work (which is a big deal, as it's a 40-minute round trip to a suitable location). I'm at a bit of a loss as to what it might be, and am asking here to see if anyone has a router-related clue. Or any ideas as to how I might go about troubleshooting this. Regards, K. -- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ ~ Karl Auer (kauer@nullarbor.com.au) work +61 2 64957435 http://www.nullarbor.com.au mobile +61 428 957160 GPG fingerprint: 9FB6 C08F 91CB 5093 30EF 3E2F 8C94 EEBD 117C 4A10 Old fingerprint: CF68 0C56 EEE4 CC19 28D4 03B3 BCE0 E800 E31F 7254 _______________________________________________ Public mailing list Public@talk.mikrotik.com.au http://talk.mikrotik.com.au/mailman/listinfo/public_talk.mikrotik.com. au---------------------------- Roger Plant