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Please add the troubleshooting information to your post To find the Troubleshooting information:

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Troubleshooting Information This page contains technical information that might be useful when you're trying to solve a problem. If you are looking for answers to common questions about Thunderbird, check out our support website. Include account names (possibly identifying information) Application Basics Name Thunderbird Version 45.6.0 User Agent Mozilla/5.0 (Windows NT 10.0; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.6.0 Profile Folder (Local drive) Application Build ID 20161222195647 Enabled Plugins about:plugins Build Configuration about:buildconfig Memory Use about:memory Mail and News Accounts ID Incoming server Outgoing servers Name Connection security Authentication method Name Connection security Authentication method Default? account2 (none) Local Folders None Normal password account3 (pop3) pop.embarqmail.com:110 None Normal password smtp.embarqmail.com:587 None Normal password true Crash Reports Report ID Submitted

All Crash Reports Extensions Name Version Enabled ID Lightning 4.7.6 true {e2fda1a4-762b-4020-b5ad-a41df1933103} Test Pilot for Thunderbird 1.3.10 true tbtestpilot@labs.mozilla.com Important Modified Preferences Name Value browser.cache.disk.capacity 512000 browser.cache.disk.filesystem_reported 1 browser.cache.disk.smart_size_cached_value 358400 browser.cache.disk.smart_size.first_run false browser.cache.disk.smart_size.use_old_max false browser.display.use_document_fonts 0 dom.apps.reset-permissions true extensions.lastAppVersion 45.6.0 font.minimum-size.x-western 11 font.name.monospace.el Consolas font.name.monospace.tr Consolas font.name.monospace.x-baltic Consolas font.name.monospace.x-central-euro Consolas font.name.monospace.x-cyrillic Consolas font.name.monospace.x-unicode Consolas font.name.monospace.x-western Consolas font.name.sans-serif.el Calibri font.name.sans-serif.tr Calibri font.name.sans-serif.x-baltic Calibri font.name.sans-serif.x-central-euro Calibri font.name.sans-serif.x-cyrillic Calibri font.name.sans-serif.x-unicode Calibri font.name.sans-serif.x-western Tahoma font.name.serif.el Cambria font.name.serif.tr Cambria font.name.serif.x-baltic Cambria font.name.serif.x-central-euro Cambria font.name.serif.x-cyrillic Cambria font.name.serif.x-unicode Cambria font.name.serif.x-western Cambria font.size.fixed.el 14 font.size.fixed.tr 14 font.size.fixed.x-baltic 14 font.size.fixed.x-central-euro 14 font.size.fixed.x-cyrillic 14 font.size.fixed.x-unicode 14 font.size.fixed.x-western 14 font.size.variable.el 17 font.size.variable.tr 17 font.size.variable.x-baltic 17 font.size.variable.x-central-euro 17 font.size.variable.x-cyrillic 17 font.size.variable.x-unicode 17 font.size.variable.x-western 14 mail.openMessageBehavior.version 1 mail.winsearch.enable true mail.winsearch.firstRunDone true mail.winsearch.global_reindex_time 1377649723 mailnews.database.global.datastore.id 7621c77f-cdf4-4ef4-b029-cefbfdcd2ff network.cookie.lifetimePolicy 2 network.cookie.prefsMigrated true network.predictor.cleaned-up true places.database.lastMaintenance 1483208224 places.history.enabled false places.history.expiration.transient_current_max_pages 104858 plugin.importedState true plugin.state.flash 0 privacy.donottrackheader.enabled true security.default_personal_cert Select Automatically Graphics Adapter Description Intel(R) HD Graphics 4000 Vendor ID 0x8086 Device ID 0x0166 Adapter RAM Unknown Adapter Drivers igdumdim64 igd10iumd64 igd10iumd64 igdumdim32 igd10iumd32 igd10iumd32 Driver Version 10.18.10.4358 Driver Date 12-21-2015 Direct2D Enabled false DirectWrite Enabled false (10.0.14393.351) ClearType Parameters Gamma: 2500 Pixel Structure: R ClearType Level: 100 Enhanced Contrast: 400 WebGL Renderer Google Inc. -- ANGLE (Intel(R) HD Graphics 4000 Direct3D11 vs_5_0 ps_5_0) -- OpenGL ES 2.0 (ANGLE 2.1.0.316930d51ea9) GPU Accelerated Windows 0 AzureCanvasBackend skia AzureSkiaAccelerated 0 AzureFallbackCanvasBackend cairo AzureContentBackend cairo JavaScript Incremental GC 1 Accessibility Activated 0 Prevent Accessibility 0 Library Versions Expected minimum version Version in use NSPR 4.12 4.12 NSS 3.21.3 Basic ECC 3.21.3 Basic ECC NSS Util 3.21.3 3.21.3 NSS SSL 3.21.3 Basic ECC 3.21.3 Basic ECC NSS S/MIME 3.21.3 Basic ECC 3.21.3 Basic ECC

re :smtp.embarqmail.com:587 None Normal password

Right click on mail account in Folder Pane and select 'Settings' Bottom of left pane select 'Outgoing server (SMTP)' select the smtp server in list. click on 'Edit' button Connection Security: select 'STARTTLS' click on all 'OK's

Close and then Start Thunderbird. Try to send and report back on results.

It worked. Thanks.